Empty lists/maps have no semantic meaning in Binding

There is a semantic difference between an empty list and a null list in Binding. Since our backing implementation is YANG-based, there is little value in this difference and hence it should be eliminated.

There are three main aspects:

1. binding runtime, which needs to turn empty lists to nulls in the Binding->DOM direction
2. binding spec, which needs to redefine how a List-based equals works, which really is defined by mdsal-binding-java-api-generator's output
3. binding runtime (again), which needs to update its equals() and translation implemenetation