Make searches case insensitive

[ojongerius]

We currently do exact matches, hence label "Foo" will not match "foo", but it probably should.

There are a few ways options, and probably more than these:

• A common approach is to lower or uppercase search string and data. Downside: terrible for performance, the database will do a sequential scan if you call lower()
• Use the citext module, which supports creating a special index. See https://www.postgresql.org/docs/current/static/citext.html
• Create indexes based on the lowercase version

Some background around edge cases to be mindful of: https://www.thedroidsonroids.com/blog/edge-cases-to-keep-in-mind-part-1-text

A very simple fix would be to use iexact for queries where case does not matter, from https://docs.djangoproject.com/en/1.11/topics/db/queries/:
Blog.objects.get(name__iexact="beatles blog"), but performance will suffer, most likely, see https://code.djangoproject.com/ticket/3575 for an interesting discussion.