Working RBAC tests!

- added waits to the related page models
- broke group, role, and user tests out of a monolithic class,
  and organized them into their own files
lint
use get_element
Merge pull request #294 from seandst/rbac-waits

Working RBAC tests!
Merge pull request #295 from dajohnso/tweak_select_dropdown

use get_element in select_dropdown*

(I'm excited to discover what gets broken by this change due to ridiculousness.)