Close #381 Meta Information in Phase Space

### Output Scaling

Uses now
![m_species c](http://latex.codecogs.com/gif.latex?m_%5Ctext%7Bspecies%7D%5Ccdot%7Ec)
to scale momentum output. (Previously it scaled by the electron mass.)

### New Attributes:
  - exclusive offset of the global moving window
    if the spatial dimension is == y
  - [p_min;p_max] + unit
  - dr + unit (spatial dimension)
  - dt + unit (time step)

### To Do

- [x] **Rebase**
We should wait for #403 being merged so I can rebase against the newest `MovingWindow` class.

- [x] **Run time test**
Check LWFA for moving window -> does the provided information work?
   -> ~~**yes**, looks quite promising :)~~ moving window seems broken (for whole sim, see gas init offset for new GPUs: repeats previous GPU plane)
   -> units ok? `UNIT_MOMENTUM` **ok**, dr **ok**, dt **ok**
   -> colorbar (charge density) unit `sim_unit` ? wouldn't just *charge* be way more clever?