Rename Util.prep Util.escape. Deprecate former.
Simplify entity-sensors.js. No need to pass this/that around so much
Delete updateSensorsNow call from entity-sensors view render()

initialise() calls loadSensorMetadata() which calls updateSensorsNow()
after metadata has loaded.
Mark MongoDBServer.HTTP_INTERFACE_URL an openable link for RendererHints
Link names in sensor table to json sensor value

* Uses values in view.sensorMetadata[sensor].actions.json
* Doesn't attempt to link if no .json exists
* Escape sensor description/type/name in template rather than via Util
Link sensor values with 'open' hints to the value
Remove actions column from sensor table

Currently the only actions are 'json' and 'open'. Json action is handled
by sensor name link and open action is handled by linking values instead.
Merge pull request #840 from sjcorbett/backlog

Improvements to entity-sensors.js