Introduce a pluggable engine and templates

[harshach]

During the deployment of a topology, we've pretty much catered for Storm way of doing things. Also during the creation of a topology, User should be able to select the engine and template ( a template is a pre-defined topology, by default we will provide a Blank template). Having Engine and Template objects will allow us to change the behavior of the TopologyEditor and also have a different deployment mode etc..