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
Fixing notifications __init__ because it was generating migration problems
Refactoring modify notifications
Refactoring email templates for notifications
Adding migrations
Fixing tests
Adding managemente command for sending pending notifications
Making notifications work synchronously by default
Removing unnecesary print
Fixing issue change body email notification template
Using iterqueryset in management command
Fixing invitation tests