Allow active class in subreddit shortcuts dropdown

When you're viewing a sub from your shortcuts bar it highlights the link
orange-red and bold, this patch simply applies the same rule to links in
the dropdown menu. Also I cleaned up the CSS selectors and removed
unnecessary !important declarations.
Making the code nicer

Removed some extra spaces from line 141, made my CSS selectors
self-descriptive by using IDs, and re-inserted !important declaration.
Merge pull request #927 from githue/subredditShortcutsActive

Add active class to subreddit shortcuts dropdown