putting EmbeddedDataStore into its own separate module

I needed to put EmbeddedDataStored and its C* deps into a separate maven
module so that it can be conditionally deployed in Vert.x. There is still a
a bunch of work to do, but this commit introduces the initial, necessary
changes. We can now introduce a config setting passed to Vert.x that will
determine whether or not to use the embedded data store.