GEARRT: misc minor updates and fixes
A bunch of small changes and small fixes that came up while I was running Iliev tests over the past few weeks.
- added some helper functions that are intended to be used for idealised tests and are referred to in the instruction on how to reproduce the Iliev tests
- removed injection of flux into particles during radiation injection. Tests show that not injecting any flux, only energy, leads to best results.
- removed a deprecated debugging check which writes out radiation and injection energies each step
- fixed some minor missed things in RT parameter example files
- cleaned up framework for stellar luminosity models. It's now easy to add new models on top of existing ones. This however required changes in all parameter files, where the stellar luminosity model now needs to be selected. Adapted documentation to reflect this.
- small fixes in some python plotting/analysis scripts.