Improve error messages for bad hashtags and project names

Summary: Ref T8509. We currently give you a fairly obtuse error when trying to name a project something like "!!". The error is correct, but not as helpful as it could be. Give users a more specific, more helpful error.

Test Plan:

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T8509

Differential Revision: https://secure.phabricator.com/D14872