Trim whitespace in tag search [#1]

after splitting on spaces, a trailing space would result in a null value
in the query params, and thus find all images.
Fix Invalidate's retry logic [#22]

Turns out I just misread the Celery documentation :(
Don't invalidate brand-new images [#25]

There's no need to make invalidation requests for newly-added images;
the invalidations are just intended to clear a stale cache.
Merge branches 'extra-arguments-on-retry', 'trailing-spaces-in-search' and 'judicious-invalidations'

Conflicts:
	tests/worker/test_invalidate.py