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.
Add split_by_n function on utils.iterators module.
Add iter_queryset method to utils.iterators module.
Add cached name and size fields to attachment model.
Change the way to generate attachment resource path.
Apply the same url naming of attachments to user photo.
Remove deprecated attachment view responsible of permission checks.
Add adhoc script for migrate the location and description/content fields to new attachments urls.
Improve attachments factories and fix tests related to storage refactor.