Standardise padding for browser directory properties widget

Author: nyalldawson

src/ui/qgsbrowserdirectorypropertiesbase.ui

@@ -11,6 +11,9 @@
    </rect>
   </property>
   <layout class="QVBoxLayout" name="verticalLayout">
+   <property name="margin">
+    <number>0</number>
+   </property>
    <item>
     <widget class="QWidget" name="mHeaderWidget" native="true">
      <property name="sizePolicy">