Removing old, currently never used code
Obsolete comments
Exception class for low level errors
Replace lowlevelError() calls with throwing exceptions
No global $app uses anymore, global functions can access $app via ResourceManager::getApp(). Early access attempt to $app throws LowlevelException
Merge branch 'master-org' into code-cleanup
Merge pull request #1582 from rixbeck/code-cleanup

No global $app uses anymore