What's Changed
* Incremental changes by freddieknets:
* `BlackAbsorber` and `K2Collimator` inherit from `xcoll.BaseCollimator` which is an `xtrack.BeamElement`
* `K2Crystal` is fully functional, automatic installation not yet
* K2 uses `Material` and `CrystalMaterial`, which both inherit from `GeneralMaterial` which is an `xobjects.HybridClass`
* Impacts are registered in `CollimatorImpacts` which is an `xobjects.HybridClass`: fully implemented for `BlackAbsorber`, partially for `K2Collimator`
* `CollimatorManager` has two new methods: `create_lossmap` and `coll_summary`; the former outputs a `dict` that is compatible with the `lossmaps` package
* Feature/aperture model check and temporary patch by giadarol in https://github.com/xsuite/xcoll/pull/15
**Full Changelog**: https://github.com/xsuite/xcoll/compare/v0.1.1...v0.1.2