Clean up forms

Add a small library to handle forms. This should make it a lot easier
to modify the form in the future as well as for other people to add
their own forms
Add action so we can delete transients
Merging v0.4 bump
Replace `update_transient()` with `set_transient()`
Output previous textarea value in the export form
Change visibility of `VIP_Scanner_Form::delete_transient()` as it's called in a hook and must be public
Merge branch 'UI-Refresh'