Moved Nested Classes into dedicated class files

In multiple locations in MD-SAL there are large nested classes, which leads to difficult reading of the source code.

This bugs should track the effort to moved nested classes out to classes dedicated for their simple purpose.

Nested classes should only be used to perform, simple, insignificant tasks (generally they are anonymous).

Each class should have a simple purpose. For example, one EXAMPLE of a class that should have its nested classes removed is:

org.opendaylight.controller.sal.binding.impl.connect.dom.BindingIndependentConnector