Fix to allow RESTCONF PUTing of Flows

- Due to a bug in the JAXB spec, which is propogated to
JAXRS, which forbids '/', even escaped, in path segments
in URLs... we can't use the nesting by refs under /flows.

- Therefore I've moved flow config to
nodes -> node -> table -> flow

- Making that change in the existing FlowConsumerImpl proved extremely
hard.  Due to the press of time I've introduced a very simple set of
FlowProvider, FlowCommitHandler, FlowTransaction, FlowTransactionValidator,
to cleanly separate the logic.  We can migrate over the validation rules as
need be.

PatchSet 11: Abstract the Transaction.  Add Groups.
PatchSet 12: Fixes for Meters

PatchSet 13: Yet another rebase

PatchSet 14: Squashing https://git.opendaylight.org/gerrit/#/c/3304/8

Must proceed: http://git.opendaylight.org/gerrit/3596/1
in openflowplugin

Change-Id: I1f1cd04a04f7a30630062725e63112cda4b049f1
Signed-off-by: Ed Warnicke <eaw@cisco.com>
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>