Added glyphicon-block class

Prevents elements moving around the page after the font file has loaded by setting a defined width on elements using the icon font.

less/glyphicons.less

@@ -29,6 +29,10 @@
   -webkit-font-smoothing: antialiased;
 }
 
+.glyphicon-block{
+  width: 1em;
+}
+
 // Individual icons
 .glyphicon-asterisk               { &:before { content: "\2a"; } }
 .glyphicon-plus                   { &:before { content: "\2b"; } }