Fix several problems, tox -e releasenotes did not run at all.
Fixes:
* Fix version import so that release note building works.
* There's no stable/mitaka branch for watcher, so remove the mitaka file,
otherwise release notes build will fail.
* Add _static directory with empty placeholder for sphinx to run.
Change-Id: Ia4dd2f7a7743dfd7f7022be04552c401ade9953f
