gxps.todo

Major:
* measure peak areas correctly
* fix crash when using some normalization methods
* peak param window does not update sometimes --- fixed??
* PseudoVoigt peak sometimes looks W-shaped (when a lot of peaks are near each other)
* handle bright mode / dark mode
* make plot customisable
* show residuals
* write tests
* improve image export
* don't crash on importing unknown files

Low priority:
* manage plot colors
* handle state.titles and view preferences in a saveable way (to .gxps or in the config?)
* improve plot update handling
* rehaul background bounds
* replace pbr dependency by importlib.metadata (requires higher python3 version)
* fine tune bus priority and event checking
* make detailed signals instead of putting everything in event properties
* use f-string interpolation (requires python3.6)
* add background types and peak shapes

Unclear if doable:
* make emitting signals a decorator
* make bus firing a decorator
* include fittable background

Unclear if it provides an advantage
* abolish the CONFIG, COLORS and dunder singletons
* use type annotations