add views for mark read and unread, view to leave discussion, modification of models to add function to leave discussion
add forgotten files
correction of markread to mark_as_reas (and unread) in urls to keep coherence between views and urls, merge of qs for DiscussionReadView and DiscussionUnreadView
tests for DiscussionLeaveView, merge of queryset in DiscussionDeletedView
correction of tests to leave a discussion
Make Discussion.delete_recipient return a Boolean instead of an Exception, fix PEP8
Merge pull request #1 from thoas/louiseDiscussion

Add more views