Overhaul css of index, course, and question pages.

Convert everything to use as much bootstrap default styles as possible.
E.g: All buttons are now bootstrap styled buttons and all of them have
an accompanying icon from font-awesome. Use bootstrap for breadcrumbs,
dropdown nav menu, etc.

Questions now clearly delineated by a box. Question title won't
disappear when user clicks to read more. Preview pane is now
distinctive. Remove use of br tags for spacing. Reposition elements for
better spacing.

Just occured to me that a search questions feature would be useful too.
CSS overhaul of answerpage.html.

Same as previous commit. Also removed unsemantic tags like <b> and
<font>.

There's a lot of code duplication for the comment sections, so there
should be some refactoring in the future.

The CSS is now getting complicated enough to warrant using sass or
something to simplify it.