EZP-20677: fixed User data not being deleted upon deletion of User Content

Also: removed unnecessary validation of $user->id (mixed not numeric)
EZP-20677: fixed throw on missing user or role assignment
EZP-20677: tested deleteUser() with mocks, removed tests duplicated in integration suite
EZP-20677: added clean up of URL aliases for deleted locations
Added reloading given $contentInfo
EZP-20677: tested deleteContent() with mocks, removed tests duplicated in integration suite
Fixed FQN in phpdoc, removed extra empty line
EZP-20677: added clearing User Content SPI cache after deleting user data
Merge pull request #298 from ezsystems/fix-EZP-20677-REST-delete-user-cleanup

Fix EZP-20677: Removing users do not clean up ezuser table and urlaliases