[FIX] Category Material nonInheritedChildren

- Closes #1315
[FIX] Session default duration for contribution

- Closes #1328
[FIX] not allow groups as contribution speakers

- Closes #1324
[FIX] Timetable caching timezone
[FIX] Unlink material/resources on deletion
[FIX] None value coming from getOwner()
[FIX] Objects with no submitter list
Merge branch 'v1.1'
[MIN] Add flask and werkzeug to requirements
[IMP] Use werkzeug dispatcher middleware
[IMP] Add flask app stub, make it runnable
[IMP] Add .wsgi file for the flask app
[FIX] Use correct Flask root_path

Thanks to indico being a namespace package flask sometimes fails at
determining the package root path correctly
[DEL] Broken/unused htdocs files
[IMP] Add routes for all the old htdocs functions
[IMP] Use request.is_secure and request.remote_addr
[MIN] Remove try..except around werkzeug import

we require it now so it's not necessary anymore
[MIN] Use git versions of flask and werkzeug
[MIN] Remove --flask option (non-flask is broken)

The legacy wsgi app is not usable anymore due to changes to make
everything work with flask. So there's no need to have it accessible
anymore.
[MIN] add absolute_import future