CSS: Use em instead of px for font size

Further, font size related settings have been moved to base.less to not create the impression that it's a good idea to change font sizes via themes.

refs #10294
refs #10295

public/css/icinga/base.less

@@ -1,5 +1,12 @@
 /*! Icinga Web 2 | (c) 2013-2015 Icinga Development Team | GPLv2+ */
 
+@font-size: 0.875em; // 14 px
+@font-size-small: 0.786em; // 11 px
+@font-weight-bold: 600;
+
+@vertical-padding: 0.429em; // 6 px
+@horizontal-padding: 0.857em; // 12 px
+
 // Make padding not affect the final computed width of an element
 html {
   box-sizing: border-box;
@@ -22,7 +29,7 @@ a {
 }
 
 blockquote {
-  border-left: 6px solid @gray-light;
+  border-left: @vertical-padding solid @gray-light;
   color: @text-color-light;
   // Reset default margin
   margin: 0;
@@ -35,26 +42,24 @@ body {
   color: @text-color;
   font-family: @font-family;
   font-size: @font-size;
+  // Set line-height w/o unit so that the line-height is dynamically calculated as font-size * line-height
+  line-height: 1.3;
 }
 
 h1 {
   border-bottom: 1px solid @gray-lightest;
-  font-size: 18px;
+  font-size: 1.286em;
   font-weight: normal;
-  line-height: 22px;
+  margin: @vertical-padding 0;
 }
 
 h2 {
   border-bottom: 1px solid @gray-lightest;
-  font-size: 16px;
+  font-size: 1.143em;
   font-weight: normal;
-  line-height: 19px;
 }
 
 p {
-  color: @text-color;
-  font-size: @font-size;
-  line-height: @line-height;
   // Remove default margin
   margin: 0;
 }
@@ -78,6 +83,6 @@ td {
 
 @media print {
   .dont-print {
-    display:none;
+    display: none;
   }
 }

public/css/icinga/themes/icinga.less

@@ -29,15 +29,6 @@
 // Text color on <a>
 @link-color: @text-color;
 
-// Font and line-height for text
 @font-family: Calibri, Helvetica, sans-serif;
 @font-family-fixed: Menlo, monospace;
-@font-size: 14px;
-@font-size-small: 11px;
-@font-weight-bold: 600;
-@line-height: 17px;
-@line-height-small: 14px;
-
-// Default padding
-@vertical-padding: 6px;
-@horizontal-padding: 12px;
+@font-family-wide: Tahoma, Verdana, sans-serif;