Fixes #3214: Multimap get & remove should return correct collection type

Fixes https://github.com/hazelcast/hazelcast/issues/3214

- Currently multimap get & remove always return list type. With this fix, they should return correct collection type depending on the configuration of multimap's value collection type.
Since `MultiMapContainer` reached check-style max method count limit, i left some room to future implementor for adding new methods and also targeting to move some none-static methods here later.