Automate the addition of licence headers to files

[DomGarguilo]

The main accumulo repo and now other accumulo-* projects automatically generate license headers for new files or update license headers for existing files. The suggestion for this ticket is to add that functionality to accumulo-proxy.

It's fine if these are ignored, but another option might be to add the license header automatically, like the main accumulo repo does.

Originally posted by @ctubbsii in #54 (comment)

If automated license headers are added, the changes made in #54 can be reverted.