Allow an user to invite friends via twitter.
Added python-twitter.
Merge branch 'devel' of github.com:matiasb/fenics into invite-a-friend

Conflicts:
	ega/urls.py
	ega/views.py
	fenics/settings.py
Fixes from review.
Merge pull request #3 from nessita/invite-a-friend

Invite a friend!