Scheduler inconsistencies in config

[jveitchmichaelis]

I've noticed a few inconsistencies with how we handle scheduler setup:

• Schema.py sets StepLR as the default, which is invalid as main checks are case sensitive (should be stepLR)
• The default in config.yaml is empty, which means that this actually falls through to ReduceLROnPlateau
• We have a config entry for crop models, but this is ignored as ReduceLROnPlateau is always used.

Questions:

• What do we want the default scheduler to be?
• Do we want to continue to enforce case sensitive checks?
• Should we handle this in the crop model as well? Either support other schedulers, or warn if the user passes an unsupported setting.