Projects - smooth out scenarios around renaming a project and slugs

Summary:
Fixes T7092. When you name project "Foo" which has primary hashtag "foo" to "Foobar", post this patch the hashtag "foo" gets added as a secondary hashtag. Also makes sure we don't normalize the hashtags in the query function as the wikimedia folks were hitting an issue around capitalization on the hashtag.

Note that T6909 remains "broken" in that you get an error that you can't do that, though if you just omit the additional hashtag it would work fine. I think if a fix is necessary here the best bet would be to simply detect this particular scenario and let things proceed; its a bit tricky though since its about two transactions about to be applied and how they interact with one another...

Test Plan: Made project "Foo" which has primary hashtag "foo". Renamed it to "Foobar" and verified "foo" was added as a secondary hashtag and "foobar" was the primary hashtag. Renamed it again to "Foo" and noted that the hashtags all ended up correct.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7092, T6909

Differential Revision: https://secure.phabricator.com/D11697