Update methods for ImpedanceModel and BeamLoadingEquilibrium

See merge request !11

The energy_loss and power_loss_spectrum methods for ImpedanceModel can now take any bunch spectrum in optional agrument.
Add bunch_spectrum and plot_bunch_spectrum to BeamLoadingEquilibrium.
Apply formatters and update notebook

Emittance calculation

See merge request !9

Merge branch 'develop' of git@gitlab.synchrotron-soleil.fr:PA/collective-effects/mbtrack2.git into develop

Add an explaination how to get non zero longitudinal cs_invariant

ci_docker

See merge request !8

+ run test suite and formatters when there is a merge request or commit on "stable" or "develop".
+ build docker image and pip package when a tag is pushed and commit on "develop".

[fix] import if dynamic versioning fails

See merge request !10

Ions

See merge request !7

1) Adds a beam_ion_effects module. Beam-ion interaction is implemented with weak-strong, strong-strong and Particle-In-Cell models.
New classes: BeamIonElement, IonParticles, IonAperture, IonMonitor
2) Adds space-charge module, implementing TransverseSpaceCharge class.
3) Adds electromagnetic fields module. Handles Faddeeva function and electromagnetic fields for space-charge and beam-ion interactions.

Other minor improvements are made to the code.

[Fix] Loading lattices with any periodicity

See merge request !6

[Fix] Issue with random sampling in PhaseSpaceMonitor

See merge request !4

Fix plotting in plot_phasespacedata