Improve cache busting for javascript files

Currently cache busting is done by appending the packaging version to but this might contain invalid characters (not supported in an URL). Change this to be a hash of the version.

In addition, configure tinymce to add cache busting to files it loads by itself and which webapp doesn't load via loader.php

This allows us to cache javascript files loaded from /client/ with the Cache-Control header. So the webbrowser caches it for us and we can skip loading ~ 21 requests on load.

This also requires a packaging change to add the cachebuster file on build

dpkg-parsechangelog -S Version  | sha1sum | cut -b 1-8> $(INSTDIR)$(WABASE)/cachebuster