Add utilities and instability folders
Change folder name from collective_effects to impedance

Import at inside the Optics.load_from_AT method to allow use of mbtrack2 without at installed.
Update load_from_AT

Main change
- Variable local_beta, local_alpha, and local_gamma are made property objects.

Minor change
- Add an option to plot phase space in different style.

Plotting routines now return figure object.

- ring has been removed from the input.
- for loop has been removed and replaced by linspace function

Two new plotting routines have been added
- plot_optics for plotting optical variables (beta, alpha, gamma, despersion)
- plot_beamdata for plotting data recorded by BeamMonitor

Class to store physical parameters
TODO: add up/down and right/left distinction for apperture

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