TranslationProject: Fix potential 500 when last_submission.unit is None
Cleanup: Remove unused parameter
Don't pass the goal slug if we don't have it
Cleanup: Avoid hitting DB unless necessary
Bugfix: Provide number of editor rows for AnonymousUser

Before this the template was setting no value for chunkSize when an
anonymous user visited the editor, and therefore they were experiencing
a JavaScript failure resulting in editor not being rendered.
Bugfix: Get the default rows count for AnonymousUser when getting units

This allows populating the editor for anonymous visitors.
Bugfix: Return empty alternative languages queryset for AnonymousUser

Otherwise the current unit is not displayed for anonymous visitors.
migrations: Raise a more appropriate error in backwards()
Migrations: Fix a dependency in pootle_store migration
Migrations: Do not dry-run 0011_update_user_to_profile

It cannot be rolled back so dry-running it is an immensely bad idea
Migrations: Handle missing constraints better
Requirements: 2.6.0 requires latest Toolkit because of placeables
Requirements: Bump up lxml requirement to match Toolkit

Because it makes no sense to provide a lower requirement since the
Toolkit is already going to pull at least lxml 2.2.0.