Pyheadtail

New features:
- RFBucket Hamiltonian supports other potentials
and fields (like space charge)
- Multiturn wakefields
- higher-order chromaticities (arbitrary order)
- dispersion supported
- unit tests
- beam optics (optics functions like the beta function as
inferred from the beam solely via statistical methods)
- full phase advance for each segment (in addition to
previous calculation of phase advance proportionally to s)
- new SliceSet interface with statistics saved at creation for the slices
and slice profile / derivative profile, also beam properties are taken over
- Bassetti Erskine space charge
- performance optimisation

**RFSystems Interface Change**
- Kick objects and Drift objects are now completely hidden behind RFSystems,
do NOT use them anymore
- all RF parameters (only!) available via

$ >>> longitudinal_map = RFSystems(...,
some_harmonics, some_voltages, some_phi_offsets, ...)
$ >>> list(longitudinal_map.voltages) == some_voltages
True
$ >>> list(longitudinal_map.harmonics) == some_harmonics
True
$ >>> list(longitudinal_map.phi_offets) == some_phi_offsets
True
- in the context of the RF parameter interface, general.utils.ListProxy
has been added
- RFBucket instances are now ONLY fixed blueprints
(same concept as for SliceSet instances).

Access the current state of the RF bucket configuration
(for Hamiltonians and matching) via

$ >>> longitudinal_map.get_bucket(some_gamma)

This release has been tested with the PS transition situation.

Attention:
It is discouraged to store slice views (blabla = rfsystems.voltages[2:4])
of the RFSystems parameter interfaces.
(Reason: their internal reference lists are not updated if
RFSystems._kicks is restructured (via pop etc))

**Minor changes / adaptions to the new, fixed implementation of the aperture module

Add losses - remove views, instead use arrays with alive particles directly.

Added 64 bit compatibility to aperture module.

- **New feature: apertures and particle losses.**
- In Wakes module:
Make function_longitudinal(..) and function_transverse(..) public and
clean up redundant code.
- In Particles: add(..) method now takes dictionary as argument.