Fix approximated longitudinal wake function sign in CircularResistiveWall

Correct scale for the exact TransverseWakeFunction in CircularResistiveWall.
Thanks to Keon Hee Kim for providing the correction factor.

The approximated longitudinal wake function in CircularResistiveWall correctly takes into account the length

Take into account length

Can compute the CSR impedance for free space and parallel plates model.
WakeFunction not implemented yet.

Allow to read both wake function and impedance with read_IW2D_folder
Fix yokoya_elliptic function

WakePotential -> add method to plot wake potential for a perfect gaussian bunch
utilities -> new function gaussian_bunch which gives the gaussian bunch profile
utilities -> read_IW2D now also reads wake function from IW2D
utilities -> new function read_IW2D_folder which reads the full results folder of IW2D into a WakeField element.
resistive_wall -> change the sign of the wake functions to agree with the code convention

The exact wake function for the transverse wake function is wrong (from paper) ! Need to find a better expression.

Correct scale in plot_wakedata
Avoid circular import by moving import in function

Add docstrings to Impedance and WakeFunction class
Rename functions for deconvolution method

Add transverse wake potential to WakePotential and move class to dedicated file
Merge Resonator and TransverseResonator into Resonator with dedicated file
wakefunction_from_imp -> change trimming to allow for a float value
wakefunction_from_imp -> transverse impedance divided by 1j, to be checked with impedance convention but ok with benchmark
Wakefield -> add wake_components

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

- Deconvolution methods in WakeFunction and Impedance class were improved.
- Analytical impedance calculation method was added to Resonator class.
- Wake potential calculation method in WakePotential2 class was corrected.

- New Wakefunction class to store a wake function object.
- New deconvolve_wp and deconvolve_imp methods were added in Wakefunction class.
- New  get-impedance method was added in Impedance class.
- New Resonator class to calculate the analytical resonator wake function.
- New Wakepotential2 class to take in wake function objects, then compute the wake potential and do the tracking.

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

- New Wakefunction class to store a wake function object.
- New deconvolve_wp and deconvolve_imp methods were added in Wakefunction class.
- New  get-impedance method was added in Impedance class.
- New Resonator class to calculate the analytical resonator wake function.
- New Wakepotential2 class to take in wake function objects, then compute the wake potential and do the tracking.

Add effective impedance calculation to ImpedanceModel
Rework plot_area to support transverse impedance and add better legend and scaling
double_sided_impedance : new function to add negative frequencies to impedance spectrums
effective_impedance : tuneS as input, use double_sided_impedance and xi input is used
beam_loss_factor : uses double_sided_impedance
Correct a few bugs in wakefield.py

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

ImpedanceModel -> new method to compute beam and bunch energy loss
beam_loss_factor -> drop 0 from data only if it is there, avoid bug if it is not

Changes in loss_factor to use frequency instead of omega
Read_CST forces to have positive real part of longitudinal impedances
New functions : Gaussian_bunch_spectrum, beam_spectrum, beam_loss_factor
ImpedanceModel.plot_area in GHz

Bugfix on ComplexData addition : sort data before interpolation
Wakefield class : Add static method to add wakefields
ImpedanceModel class : add methods to handle more easily the wakefields. Maybe can be improved more by using a single Wakefield of each type ?
ImpedanceModel class : add plot_area and summary. summary to be improved more

Add Yokoya_elliptic function to compute Yokoya factors for an elliptic shape.
Add an option to divide by value in read_CST
Add docstrings to read_CST and read_IW2D

Add a ImpedanceModel object which derives from Element and is used to sum up different Wakefield elements
Fix uppercase module in resistive_wall.py

Circular and rectangular tapers
Correct module name in tools.py
Add kick factor calculation for quadrupolar wakes (similar to dipolar ones)

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