setup: Run migrate non-interactively
Syncing with core: Add creation_time and screenshot_search_prefix fields to Project
Syncing with core: Rename sync_time field to file_mtime in Store
Syncing with core: Add creation_time, last_sync_revision and obsolete fields to Store
Syncing with core: Minor adjustment to TMUnit drop migration
Syncing with core: Drop djblets SiteConfiguration database table

Note that this doesn't remove the djblets code because it is required
to provide upgrade paths from ancient Pootle releases.

Since 2.6.0 is meant to be a transitional package the code will be
gone when the next release (possibly 2.7.0) is installed immediatly
after upgrading to 2.6.0.