JSON v2 - serialize label params

[radumereuta]

Fixes: #2522
Fixes: #1509

[ehildenb]

You'll have to add a KLabel class to kast.py in pyk, and modify KApply to use this class directly. I would really like it if this still worked: KApply('some_symbol', [args]), so taht we don't always have to supply sort params. So KApply(KLabel('some_symbol', sort_params), [args]) is also possible.

Then you need to modify the from_dict and to_dict functions of each KInner that is affected.

https://github.com/runtimeverification/k/blob/master/pyk/src/pyk/kast.py