Xplt

What's Changed
* Add LICENSE by eltos in https://github.com/xsuite/xplt/pull/3
* Replace np.float with builtin type float by milo-gsi in https://github.com/xsuite/xplt/pull/6
* Minor fixes

**Full Changelog**: https://github.com/xsuite/xplt/compare/v0.7.0...v0.7.2

- Add support for thick elements in Floor Plot by giadarol
- More options for FFT Plot
- Matplotlib stylesheet

**Full Changelog**: https://github.com/eltos/xplt/compare/v0.6.0...v0.7.0

- Improve property handling and introduce derived properties
- Drops `xplt.units` module in favour of `xplt.properties`
- Drops `xplt.register_property` method in favour of `xplt.register_data_property` and `xplt.register_derived_property`
- Drops `wrap_zeta=True` keyword argument in favour of property `zeta_wrapped`
- For details, see https://eltos.github.io/xplt/examples/properties.html
- Improved consistency
- Make pandas an optional dependency
- Renamed `metric=` keyword argument of `TimeVariationPlot` to `kind=`

**Full Changelog**: https://github.com/eltos/xplt/compare/v0.5.0...v0.6

- Update examples to match latest xtrack API
- Usage improvements and simplification

Full Changelog: https://github.com/eltos/xplt/compare/v0.4.1...v0.5.0