Revise LICENSE and NOTICE following mentor feedback

See:
https://mail-archives.apache.org/mod_mbox/incubator-brooklyn-dev/201412.mbox/%3C20141211165910.GG36553%40Chips-MacBook-Air.local%3E

MIT/BSD licensed subcomponents now credited in LICENSE instead of
NOTICE. Reviewed ASL2 credits in NOTICE; determined that they do not
have their own NOTICE file, and therefore there is no need to mention
them, per https://www.apache.org/dev/licensing-howto.html#alv2-dep.
This meant that there were no credits remaining in NOTICE; replaced
NOTICE with boilerplate recommended by
https://www.apache.org/dev/licensing-howto.html#simple.
This closes #390

* github/pr/390:
  Revise LICENSE and NOTICE following mentor feedback