Share course options

Share course options: Twitter, Facebook, email. Messages and links
adapted to UJI.

From the original source comments:

## TODO: this should probably be an overrideable block,
##       or something allowing themes to do whatever they
##       want here (and on this whole page, really).
Favicon UJI
Merge pull request #3 from carlesbellver/master

Share course options adapted to UJI