Enable wasm mint bindings (CosmWasm#1445)

Closes / Related to: CosmWasm#1029

## What is the purpose of the change

Re-instate the CoswmWasm message handlers for Mint and FullDenom. Related to osmosis-labs/bindings#25 on the Rust side.


## Brief change log

  - Uncomment the Mint-related code.
  - Implemented `Mint` using `TokenFactory`.
  - Implemented `FullDenom` in terms of `TokenFactory`.

## Testing and Verifying

Uncommented and adapted already existing tests.


## Documentation and Release Note

  - Does this pull request introduce a new feature or user-facing behavior changes? (yes. For the CosmWasm side)
  - Is a relevant changelog entry added to the `Unreleased` section in `CHANGELOG.md`? (will do)
  - How is the feature or change documented? (not documented)

keeper/keeper.go

@@ -79,7 +79,7 @@ func (k Keeper) GetCreatorPrefixStore(ctx sdk.Context, creator string) sdk.KVSto
 	return prefix.NewStore(store, types.GetCreatorPrefix(creator))
 }
 
-// GetCreatorPrefixStore returns the substore that contains a list of creators
+// GetCreatorsPrefixStore returns the substore that contains a list of creators
 func (k Keeper) GetCreatorsPrefixStore(ctx sdk.Context) sdk.KVStore {
 	store := ctx.KVStore(k.storeKey)
 	return prefix.NewStore(store, types.GetCreatorsPrefix())