New LongRangeResistiveWall class to deal with multi-bunch and multi-turn wakes from resistive wall.
Add Mpi.share_means method to share bunch means using MPI.

Add CavityResonator class
Add BeamLoadingVlasov class, to do tested and developped further.
From BeamLoadingVlasov, only the beam_equilibrium method is well tested and benchmarked.
The cannonical_transform and solveB methods have to be tested and benchmarked further.

A method to compare energy loss from a wake potential to a loss factor.
Minor changes :
- sigma method in Ring object has been edited.
- add WakePotential in __init__ in tracking module.

Remove tools.py to avoid circular import problem with wakefield.py -> merged into wakefield.py
Remove machines folder to save machine data in a seperate git instance
Rework import so the code can be used as independant module mbtrack2

Update machines/__init__.py, machines/soleil.py, tracking/__init__.py, tracking/aperture.py, tracking/element.py, tracking/optics.py, tracking/parallel.py, tracking/particles.py, tracking/rf.py, tracking/synchrotron.py files