Separate base UI test classes for project and site app views

[mikkonie]

The current UITestBase base test class sets up a lot of project-specific data, which is irrelevant to site apps (or can be set manually in app test class setUp(). We should separate project and site app base test classes.

This will be a breaking change as moving the setup of certain variables from the current class will require changes in test implementations. It must be documented accordingly.