Implementation of DeallocateFlowAction in SDNNetwork internal driver.

http://jira.i2cat.net:8080/browse/OPENNAAS-1119
DeallocateOFFlow method in OFProvisioningNetworkCapability checks given flow exists before deallocating it, and removes it from sdnnetwork model after deallocation has taken place.

http://jira.i2cat.net:8080/browse/OPENNAAS-1118
Descriptions for newly created classes.
Merge pull request #703 from isartcanyameres/feature/sdnnet-deallocate-flow

Feature/sdnnet deallocate flow