Add wait for changing display name, change edit page inheritance

This is to attempt to solve the intermittent failures on saucelabs jobs by adding a wait. It also fixes inconsistencies with which page model is used in checks as well as changes inheritance of edit page to inherit from base. @bobsilverberg r?
Oh, the wait itself is in the base.py, I wasn't sure how to incorporate it into the action as it would be tedious to always need to pass in a username before clicking the save button.