Refactoring

## DONE
* integration with rOCCI-core 4.0.0
* new, modular authN
* better handling for VOMS credentials
* general refactoring and code clean-up

## ToDo
* rOCCI-core 4+ specific functionality (mixin creation, new attribute handling etc.)
* full OCCI-OS support (still not tested properly)
* code clean-up and documentation updates