add font awesome 3.2.1 files
add icons to Documentation, Source, and Issues buttons on plugin pages

- Added Font Awesome CSS to ApplicationResources (replaces Bootstrap Glyphicons) and added icons to buttons on plugin pages
- Removed Glyphicons (bootstrap-sprites.less) from style.less
- Refactored buttons GSP code into common _pluginButtons template
Merge pull request #32 from kenliu/add-link-icons

Add icons to button links on plugin list pages and plugin detail page