Provide image with epics-base only

[ericonr]

This is useful for anyone who wants to have access to {ca,pv}{get,put,monitor} tools without installing them locally.

It might also be useful to provide a script to access these tools inside the container without having to do so manually. (I don't know if that belongs in this project, though)

Anyone who wants to use makeBaseApp/other tools should consider installing the full image, though.