New Plugin: Phase Space

## I am writing this pull request message right now, please lean back and come back later :)

This plugin introduces a live [phase space](https://en.wikipedia.org/wiki/Phase_space#Examples) analysis.

*More Images - explain reduce algorithm*

### User Documentation:
For an introduction how to use it I will add a new page to our [wiki](https://github.com/ComputationalRadiationPhysics/picongpu/wiki/PIConGPU-Plugins) in the next hours.

### Dependencies:
- output in *parallel libSplash* format

### Current limitations:
- works only in 3D right now
- only one range per selected space-momentum-pair possible right now (naming collisions)