Django-comments-tree

* Use `django.core.signing` with temporary comment passed in URL
redirection.
* Fix mistakes in documentation.

* App translation to French thanks to Brice Gelineau.
* Fixed MANIFEST.in file, so that files with translations are
distributed.

* Javascript plugin (based on ReactJS).
* Web API to:
* Create a comment for a given content type and object ID.
* List comments for a given content type and object ID.
* Send feedback flags (like/dislike) on comments.
* Send report flag (removal suggestion) for a comment.
* Template filter `has_permission` applicable to a user object and
accepting a string specifying the `app_label.permission` being
checked. It returns `True` if the user has the given permission,
otherwise returns False.
* Setting `COMMENTS_XTD_API_USER_REPR` defines a lambda function to
return the user string representation used by the web API in response
objects.
* Setting `COMMENTS_XTD_APP_MODEL_PERMISSIONS` to explicitly define what
commenting features are enabled on per app.model basis.
* Templates `comments/delete.html` and `comments/deleted.html` matching
django-comments-tree default twitter-bootstrap styling.
* Dependencies on Python packages: djangorestframework.
* Supports i18n for English and Spanish.
* All settings namespaced inside the COMMENTS_XTD setting.
* Management command to migrate comments from django-contrib-comments to
django-comments-tree.
* Enable removal link in `django_comments_tree/comment_tree.html` when the
user has the permission `django_comments.can_moderate`.
* Changed, when the user logged has `django_comments.can_moderate` permission,
template `django_comments_tree/comment_tree.html` will show the number of
removal suggestions a comment has received.
* Changed, when a comment is marked as removed by a moderator
(using django-comments' `comments-delete` url) every nested comment below
the one removed is unpublished (`is_public` attribute is turned to
`False`).
* Changed view helper functions, `perform_like` and `perform_dislike` now
returns a boolean indicating whether a flag was created. If `True` the flag
has been created. If `False` the flag has been deleted. These two functions
behave as toggle functions.
* Changed templates `comments/preview.html`, `comments/flag.html` and
`comments/flagged.hml`.
* Removed dependency on django-markup.
* Removed template filter `render_markup_comment`.
* Removed setting `MARKUP_FALLBACK_FILTER`.

Update travis.yml to install gdal. Solves a build issue.

Add a comment count template view.

Add data migration to insure that the 'assoc' value is set in the TreeComments

Added a Manager method: user_flags_for_model

This method uses the Postgres only ArrayAgg, if Postgres is available.
This also required me to expand my checking so that the module can still work if postgres is
not used. This will require some more elaborate testing in the future, if I want to test with postgres
and without. I'll likely test locally with postgres