Voting: Drop voting

It is largely unused. django-voting is also incompatible with custom user
models.
Changelog: Fixed wording
Changelog: Mention voting being dropped
Changelog: Update expected release date
staticpages: Use lazy User foreign key
requirements: Update some requirements

We were affected by a nasty South bug in legalpage migrations.
https://stackoverflow.com/questions/20446724
Requirements: Update Tastypie requirement

Necessary to avoid some warnings, to get a lot of bugfixes and to
have a recommended version.
Travis: Disable pytest
requirements: Update Django requirements
requirements: Update various requirements versions

Also drop exact versions for travis as we will always want the latest ones.
requirements: Update Raven optional dependency to 5.x
Travis: Always use latest packages from pypi
Travis: Use travis_retry for installing things
Travis: Cache apt packages
settings: Remove the INTERCEPT_REDIRECT option from dev settings

The option is deprecated on newer versions of django-debug-toolbar
Upgrade: Fix pootle imports
Permissions: Use User over PootleProfile
Permissions: Use User in get_matching_permissions()
Permissions: Change check_profile_permission() to check_user_permission()
Permissions: Minor style fixes