Improve user-facing text messages

Some of the text in the module is unclear for end users. In some cases it's either a bit too informal, or only contains "something is wrong" not "something is wrong, here's how to fix". In our case, we're using Masquerade to allow non-technical users to switch between franchise accounts when a single person owns multiple franchises, so we need to make the text as clear as possible.

I'm open to suggestions on any of the text strings that have been modified, plus any which haven't been changed.