Streamline some tests

Move logic testing of validators from the UI tests to unit.
Don't test Hibernate email logic.
Add a small check on goToHome to make sure we actually got home.
Remove RetryRule - was causing more problems than it fixed, such as altering failure reasons and hiding real failures.
Add webhooks to test plan, move project tests to separate class.
Shift login actions to a single step where possible.
Having a good set of valid and invalid username and slugs is excellent, but this doesn't seem like the right place to test all of them.  Perhaps we ought to test, end to end, one valid and one invalid example of each here in `functional-test`, and move the other test values to fast-running unit tests in `zanata-server`.  Then, if the validator class becomes broken, the responsible developer will find out much sooner.