Create formal class for settings objects

[jwildfire]

Summary

We should figure out the best way to store default settings objects (and possibly consider making a real class for these objects)

Current State

The default settings for edish (and eventually other charts) are hard coded as lists in generateSettings()

Future State

Default setting objects are saved as individual files - possibly in data\ or a subfolder thereof - and imported as needed in generate settings. We might also want to create a formal R6 class for settings. If we go that route, several of the existing functions - getSettingValue(), setSettingsValue() - could be converted to R6 methods.

[jwildfire]

I'm leaning towards not building a unique class at this point, but definitely want to go ahead and save the default setting lists as standalone files. Seems like this is easy enough to tackle with save() functions.

[jwildfire]

Going to attempt to fully define settings objects using the metadata infrastructure in v0.10.0, so the conversation regarding storing the shell objects will be irrelevant. Changing issue to just cover creating a more formal class (which is currently a low-ish priority)

[jwildfire]

Not a bad idea to make the settings a formal class with associated methods, but this would be a major refactor and I think we're far enough along with the metadata that this can be marked as don't fix.