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

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.

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

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

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