Tag Settings Menu Autosave

closes #4517

- adds autosave to name/slug/description fields in TSM
- adds nprogress indicator when saving
You've already got this value in the `name` parameter that you trimmed earlier.

If you just allow the other saveActiveTagSlug/Description methods to *set* their respective properties (just not save if name is blank) you won't have to do this "ah crap get all the scratches guys!" logic, and can instead just make this method work the same way as the others, offering us even more of an opportunity for abstraction in the `saveActiveTag` method, weeeee!