UX improvements to photo, web view and external resource widget config

- Better explanatory text
- Change '0' values to 'Auto'
- Ad 'px' suffix to values
- Allow resetting sizes to Auto with clear button

Author: nyalldawson

src/ui/editorwidgets/qgsexternalresourceconfigdlg.ui

@@ -45,7 +45,7 @@
       <property name="geometry">
        <rect>
         <x>0</x>
-        <y>-206</y>
+        <y>-210</y>
         <width>465</width>
         <height>621</height>
        </rect>
@@ -316,9 +316,12 @@
            </widget>
           </item>
           <item row="2" column="2">
-           <widget class="QSpinBox" name="mDocumentViewerHeight">
+           <widget class="QgsSpinBox" name="mDocumentViewerHeight">
+            <property name="specialValueText">
+             <string>Auto</string>
+            </property>
             <property name="suffix">
-             <string/>
+             <string> px</string>
             </property>
             <property name="prefix">
              <string/>
@@ -329,7 +332,13 @@
            </widget>
           </item>
           <item row="1" column="2">
-           <widget class="QSpinBox" name="mDocumentViewerWidth">
+           <widget class="QgsSpinBox" name="mDocumentViewerWidth">
+            <property name="specialValueText">
+             <string>Auto</string>
+            </property>
+            <property name="suffix">
+             <string> px</string>
+            </property>
             <property name="maximum">
              <number>10000</number>
             </property>
@@ -345,7 +354,7 @@
           <item row="1" column="3" rowspan="2">
            <widget class="QLabel" name="label_2">
             <property name="text">
-             <string>Specify the size of the preview. If you leave it set to 0, an optimal size will be estimated.</string>
+             <string>Specify the size of the preview. If you leave it set to Auto, an optimal size will be calculated.</string>
             </property>
             <property name="wordWrap">
              <bool>true</bool>
@@ -384,6 +393,13 @@
    </item>
   </layout>
  </widget>
+ <customwidgets>
+  <customwidget>
+   <class>QgsSpinBox</class>
+   <extends>QSpinBox</extends>
+   <header>qgsspinbox.h</header>
+  </customwidget>
+ </customwidgets>
  <tabstops>
   <tabstop>scrollArea</tabstop>
   <tabstop>mRootPath</tabstop>

src/ui/editorwidgets/qgsphotoconfigdlgbase.ui

@@ -41,7 +41,13 @@
        </widget>
       </item>
       <item row="1" column="1">
-       <widget class="QSpinBox" name="sbWidgetWidth">
+       <widget class="QgsSpinBox" name="sbWidgetWidth">
+        <property name="specialValueText">
+         <string>Auto</string>
+        </property>
+        <property name="suffix">
+         <string> px</string>
+        </property>
         <property name="maximum">
          <number>10000</number>
         </property>
@@ -55,9 +61,12 @@
        </widget>
       </item>
       <item row="2" column="1">
-       <widget class="QSpinBox" name="sbWidgetHeight">
+       <widget class="QgsSpinBox" name="sbWidgetHeight">
+        <property name="specialValueText">
+         <string>Auto</string>
+        </property>
         <property name="suffix">
-         <string/>
+         <string> px</string>
         </property>
         <property name="prefix">
          <string/>
@@ -70,7 +79,7 @@
       <item row="0" column="0" colspan="2">
        <widget class="QLabel" name="label">
         <property name="text">
-         <string>Specify the size of the preview. If you leave it set to 0, an optimal size will be estimated.</string>
+         <string>Specify the size of the preview. If you leave it set to &lt;i&gt;Auto&lt;/i&gt;, an optimal size will be calculated.</string>
         </property>
         <property name="wordWrap">
          <bool>true</bool>
@@ -82,6 +91,13 @@
    </item>
   </layout>
  </widget>
+ <customwidgets>
+  <customwidget>
+   <class>QgsSpinBox</class>
+   <extends>QSpinBox</extends>
+   <header>qgsspinbox.h</header>
+  </customwidget>
+ </customwidgets>
  <resources/>
  <connections/>
 </ui>

src/ui/editorwidgets/qgswebviewconfigdlgbase.ui

@@ -42,7 +42,13 @@
     </spacer>
    </item>
    <item row="1" column="1">
-    <widget class="QSpinBox" name="sbWidgetWidth">
+    <widget class="QgsSpinBox" name="sbWidgetWidth">
+     <property name="specialValueText">
+      <string>Auto</string>
+     </property>
+     <property name="suffix">
+      <string> px</string>
+     </property>
      <property name="maximum">
       <number>10000</number>
      </property>
@@ -56,9 +62,12 @@
     </widget>
    </item>
    <item row="2" column="1">
-    <widget class="QSpinBox" name="sbWidgetHeight">
+    <widget class="QgsSpinBox" name="sbWidgetHeight">
+     <property name="specialValueText">
+      <string>Auto</string>
+     </property>
      <property name="suffix">
-      <string/>
+      <string> px</string>
      </property>
      <property name="prefix">
       <string/>
@@ -83,6 +92,13 @@
    </item>
   </layout>
  </widget>
+ <customwidgets>
+  <customwidget>
+   <class>QgsSpinBox</class>
+   <extends>QSpinBox</extends>
+   <header>qgsspinbox.h</header>
+  </customwidget>
+ </customwidgets>
  <resources/>
  <connections/>
 </ui>