Fix Parameter change via proposal

[alpe]

Scenario:

Change value for the instantiateAccess parameter from AccessTypeOnlyAddress with an address to a value without address like AccessTypeNobody.

Issue

It fails with invalid parameter value: address not allowed for this type.

Cause

The address part from the previous state was not cleared by the gov parameter change proposal handler. Probably because it is set to an empty value.

This can be replicated in a modified TestUpdateParamsProposal test.

[alpe]

@bragaz fyi: you may run into this with simulations

[leobragaz]

During the weekend I've tried to solve this but somehow it kept returning this error so this morning I asked my @RiccardoM to help me debug the code.
We found out that protobuf takes care of the unmarshal while we were using json.Marshal to encode the CodeUploadAccess param inside ParamChanges.
After switching to protobuf marshaler everything worked fine.
However, the tests will fail due to a bug inside the Capability module but I don't think this is related to the wasm params.