at is kept as a "soft" dependency

Fix ADTS implementation in TransverseMap and TransverseMapSector to use Jx/Jy instead of x/y.
Add Synchrotron.get_adts function which compute ADTS from AT lattice.
Change Synchrotron class docstring regarding ADTS.

move down init

Fixed error on the computation of the beam size with dispersion in Synchrotron.sigma method.
Add import of plot_beamspectrum and streak_beamspectrum

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.

Fix mbi_threshold to have sigma in [s}
Add plot_critical_mass to instabilities (ions)
Add sigma(position) to synchrotron to compute the beam size at any ring location

Add ABI threshold calculation
Bugfix synchrotron_tune computation
Add zoom option to ImpedanceModel.plot_area

Add T1 = RF period to synchrotron object
Add binning and plot_profile to Bunch object // plot_profile to improve
Modify beam.filling_pattern to store the array instead of computing it every time
Add distance_between_bunches method to Beam object
Modify not_empty method of Beam to use filling_pattern

Optic functions as arrays
Uses PyAT lattice for import
Adapt other files for the change

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

To be PEP8 complient:
Lowercase folders
Extended docstrings
Rename and divide some files

Add synchrotron radiation in transverse plane
Fix a mistake in the transverse one turn map

New parallel module to handle Mpi class which is used in Beam

Test OK, to improve