Delete comments functionality
Merge pull request #67 from taigaio/delete-comments

Delete comments functionality
Changed the project templates descriptions
Fix wrong assignation of invited_by field on invitation creation process (fix #958)

Additionally it replaces the hack (django < 1.7) of double foreign key
on intermediate table (n2m relation) with trully foreign key (django 1.7
now supports it) adding corresponding migrations for conseve all previous
data.
Increment size of username and email field of user and add unique=True to email.