Started a cleaning up of the PML export infrastructure.

Idea is to get rid of the Passes that operate only on functions,
and base the whole structure on Module passes only.

This commit:
* Removed PMLExportPass and PatmosExportPass
* add "main" if roots are empty, directly in PMLModuleExportPass
  - this is ugly and demands for a cleaner solution
Cleaned up class hierarchy of PMLExport & friends
Reintroduced loop information for PML exports
DefaultRoot for PML Export now in Patmos TM

* DefaultRoot "main"