Start reworking test case layout

Move API helpers to separate class
Get rid of intermediate interfaces
Add facility to auto clean up created resources so test case code is
shorter.
Convert TestGetWall.php to new test case layout
Convert TestCreateWall.php to new test layout
Convert TestSessions.php to new test framework
Convert TestSetWall.php to new test layout
Convert TestUserSummary.php to new test layout
Remove unneeded abstract test case classes