Lofar-h5plot

**Updates**
* Iterate through time and frequency (if applicable) with buttons.
* Support changing station lists between solsets/soltabs.

**Bugfixes**
* Load the first solset rather than `sol000` specifically.

**General notes**
* More documentation for classes/functions.
* Start separating plotting logic from the rest, so things are less intertwined.

+ Added support for multiple SolSets (or rather proper handling).

* Less crashes for clock and RM type SolTabs.

Fixed plotting `rotationmeasure` crashing the application.

First production ready (hopefully) release.

Support for plotting `amplitude`, `phase`, `rotation` and `polalign` against time or frequency and `rotationmeasure` against time.

Axes are reordered at runtime, plotting should be faster now.

Let's break it again.

Bug with axes order fixed.
Phase wrapping checkbox disabled for now.

Initial release of H5Plot. Feel free to break it!