Display recently edited posts per project #317

Five most recently touched posts by the logged in user are displayed in the sidebar, along with their status (`added`, `modified`, `renamed` or `removed`). Recent file list is cached in `localStorage` for the current branch, and updated when the user switches to a different repository or branch, or when the cached data becomes invalid (`Last-Modified` header is cached and compared to remote using the `If-Modified-Since` header for a [conditional API request](http://developer.github.com/v3/#conditional-requests)).