Add methods that allows registering any serializer

Add methods that allows registering any serializer

Add new methods to SwitchConnectionProviderImpl that will allow us
to register any type of OFSerializer and OFDeserializer, so we will
be able to for example register serializers for OpenflowPlugin models
directly in OpenflowPlugin, without requiring changes in
OpenflowJava.
Change HeaderSerializer and HeaderDeserializer to require DataContainer
instead of DataObject.

See also: bug 7136

Change-Id: I002cb787a6db61d864e205d99fafa54692e220a6
Signed-off-by: Tomas Slusny <tomas.slusny@pantheon.tech>