Avoid using ResourceManager to get the resource a capability belongs to.

Capabilities already have a reference to the resource they belong to.
Using this reference helps keeping the code clean :)
Implement removeOpenflowForwardingRule method, calling REMOVEOFFORWARDINGRULE action.
Process action execution exceptions in executeAction method.
Refresh model with real flows after creating and removing a flow, and before returning all flows.

TODO: Implementation of the refreshModelFlows method.
Implement refreshModelFlows method in OpenflowForwardingCapability.
Add author
Don't populate the model in createOFForwardingAction. The capability takes care of populating it using another action.
Assert messages for createOpenflowForwardingRuleTest.
Mockup GetFlowsAction to make tests fail in a comprehensive way.
Merge pull request #697 from isartcanyameres/feature/removeOFfwdRule

Feature/remove offwd rule