consolidate scala license headers

@aemoncannon you'll need to merge (or say this is ok) as it touches the license files.

I have gone through all the scala headers and copied the various licenses into a single LICENSE file at the top level. This means that we can fulfil our obligations of distributing the license file with binary distributions (which we technically weren't doing, eek!).

Since the information is then clearly available in the LICENSE file, I think it is nice to remove the duplication from individual files. It means that we don't have to keep the individual files updated as new contributors add to the files.

This only relates to the server licenses, since the elisp will be moved into a separate repo soon.

closes #416