Replace the glyphicons with font awesome icons

There are still some scss mixins that use the old (from bootstrap 2)
image icons. Replacing them will have to be done in a separate patch.

I also link to the css file, instead of scss, because django-pyscss has
some problems finding the right file. This is reported and will have to
be fixed upstream to unbundle bootstrap.

Change-Id: I67e94a9283bcceef8fc89343f3f5b2d7e0d4449f
Partial-implement: blueprint font-icons-replace