We now check the subsite state for the context and validate it against the current member's
group permissions using the SilverStripe ORM relationships instead of using SQL queries.
More granular permission checks e.g. canView etc are still up to data models to define and
handle.
- moving all phpunit tests into tests/php
- moving all extensions from _config.php into config.yml and removing obsolete _config.php
- moving GridFieldSubsiteDetailForm_ItemRequest into own file
(cherry picked from commit ee02828)
