feature(client): Error and tooltip fixes!

* Hide errors on form change if form is valid. Help with issue #765 where "Incorrect password" error is shown even after the user updates the password.
* Prevent form re-submission while form is disabled.
* Allow tooltips to be displayed when clicking "next" button even if form is disabled.

fixes #765
fixes #858
Merge pull request #839 from mozilla/issue-765-remove-error

feature(client): Error and tooltip fixes!