Fix some errors in sample_data command
Adding raven requirement
Merge pull request #135 from taigaio/us/1380/sentry

Adding raven requirement
Adding support for extra text in invitation
Merge pull request #136 from taigaio/us/1396/extra-text-for-inviting-users

Adding support for extra text in invitation
Add proper validation of watchers for issues, tasks and userstories serializers.
Add CONTRIBUTING.md file.
Merge pull request #139 from taigaio/contributing

Add CONTRIBUTING.md file.
Fixing task tests
Merge pull request #138 from taigaio/watchers-validation-bug

Add proper validation of watchers for issues, tasks and userstories serializers.
Removes redundant FIXME

 * Removes a Choice that has already been moved to the .choices module
Merge pull request #140 from entrepreneurj/models/choices/cleanup

Removes redundant FIXME
Update django version to 1.7.1
Merge pull request #141 from taigaio/django-version-update-bugfixes

Update django version to 1.7.1
Remove api/v1/projects/XX/tags call (Not necessary)
Fixing notifications __init__ because it was generating migration problems
Refactoring modify notifications
Refactoring email templates for notifications
Adding migrations
Fixing tests