Add new nvidia functors

For Multiplication/Products and Substraction
Add Background Fields for Particle Pusher
Add const declaration for getter

Caused some error with DataSpace<> += getter * uint later on
Add option to run over GUARD too

- particle pusher: we do not want do communicate,
  add the field for interpolations in my own guard
- cellwiseOperation: calculate the right total/physical offset
  transparently for each AREA the user specifies
Fix Influence Flag
Clean up Documention and Interfaces

- use functor
- add/update documentation
- change example to disabled
- use simDim