2.3.0.201804120154: Gzip resources; optional rule engine dependency

- Add an option to serve prebuilt gzipped web app
  resources and add a Content-encoding: gzip header
  to the response.  This reduces significantly the
  initial download size of the web app. Enable in
  Paper UI (Configuration > Services > UI > HABot).

  NOTE: myopenhab.org/openHAB Cloud does NOT support
  reverse proxifying with Content-encoding: gzip, so
  enabling option will NOT work with this service.
  Use your own reverse proxy (ie. nginx) or another
  method.

- Make the dependency to the rule engine optional
  (org.eclipse.smarthome.automation). The action
  type module will be enabled only if the automation
  engine bundles are already installed.

- HbBtn: fix command expression parsing

- Small cleanups in Javadoc & quasar.conf.js.

Signed-off-by: Yannick Schaus <habpanel@schaus.net>