Improvements to entity-sensors.js

* Link sensor names to their JSON values
* Link sensor values with 'open' rendering hints to the sensor value
* Removed Actions column from sensor table
* Deprecates `Util.prep` in favour of `Util.escape`.
* General tidy of passing of this/that around. (`_.bindAll(this)` means there's no need to pass `this` to other functions on the view.)

Also adds a renderer hint to MongoDbServerImpl to link to a server's HTTP interface URL.