Jumbotron: remove the hard-coded font-size from jumbotron.less and moved it...

Jumbotron: remove the hard-coded font-size from jumbotron.less and moved it into variables.less where other .font-size-xxxxx things now live.

less/jumbotron.less

@@ -6,7 +6,7 @@
 .jumbotron {
   padding: @jumbotron-padding;
   margin-bottom: @jumbotron-padding;
-  font-size: (@font-size-base * 1.5);
+  font-size: @font-size-jumbotron;
   font-weight: 200;
   line-height: (@line-height-base * 1.5);
   color: @jumbotron-color;

less/variables.less

@@ -368,8 +368,8 @@
 @jumbotron-padding:              30px;
 @jumbotron-color:                inherit;
 @jumbotron-bg:                   @gray-lighter;
-
 @jumbotron-heading-color:        inherit;
+@font-size-jumbotron:            ceil(@font-size-base * 1.50); 
 
 
 // Form states and alerts