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