Submit and/or Runtime checking of YAML inputs

We discussed this during our most recent dev-call. There are 2 feature requests:

1. Allow for case-insensitive yaml parameters. Right now yaml variables are ignored if they are not the exact correct key, which includes case sensitive. For example `Frequency` will work for a output yaml file. `frequency` will not. Is there functionality in EKAT for `params.get<>()` to treat the key as case insensitive?
2. Often for output yaml files a typo or unexpected behavior might not get detected until runtime, and sometimes even deep into the run, for example with monthly restarts. The example we discussed today was a parameter that wasn't being used (because it was written w/ the wrong case) which didn't pop up as a problem until deep into the run because it was a monthly output. If we had a yaml checker that could alert users to keys that are unused, for example comparing against a master list, this might avoid wasted cycles.