Fix link to #2895.
Update Font Awesome to v4.2.0.
Remove the unused fontawesome-webfont.eot.
Fix `transition` property.

http://caniuse.com/#feat=css-transitions
Merge pull request #2898 from XhmikosR/font-awesome
Update history to reflect merge of #2898 [ci skip]
Merge pull request #2899 from XhmikosR/master
Update history to reflect merge of #2899 [ci skip]
Add SASS mixins and use them.

Reduces code duplication and makes things cleaner.