Separate Cupper (the Hugo instance) from the Cupper theme

[aral]

Currently the Cupper Theme is tightly coupled to an instance of Hugo that includes the sample Cupper content. These two should be separate so that the Cupper theme can be developed without dependencies on the snapshot of the Hugo source that it’s based on. (Otherwise, as Hugo improves, you will have to incorporate those changes into Cupper manually.)

As per the previous few issues I just opened, look at the Hugo Learn Theme for an example of how this would work.