Simplify namespacing?

A bit related to #1 (closed), but the namespacing appears a bit cumbersome. i.e. there is

• LOFAR::StationResponse (which is pretty much used throughout all of the code)
• LOFAR::BBS (which seems hardly used)

So can we just reduce/merge LOFAR::StationResponse and LOFAR::BBS to LOFAR namespace (and eventually everybeam namespace)? What do you think @tol @offringa