Fixed PIC parameter setting

- Now PIC grid is calculated only in the area where field is correct.
- 'field limit' in model parameter dictionary is now in modelling units.
- Fixes to get_pic_distribution.py
Fixed spacial field distribution tool
Fixed coefficients for field calculation

- Fixed coefficient calculation (it was completely broken);
- Moved all the coefficient calculation to settings/configfiles.py;
- Fixed graph building - correct units and axis;
- "M number" is now a number of momentae inside sphere.