Small improvements, mostly to documentation.

A note on the change to entity-summary.js: calling updateWithData with no arguments is equivalent to calling updateWithData(undefined), which makes updateWithData's call to 
```that.revealIfHasValue("service.isUp", that.$(".serviceUp"), null, data)```
equivalent to the call deleted from updateSensorsNow: 
```this.revealIfHasValue("service.isUp", this.$(".serviceUp"))```

revealIfHasValue's behaviour is the same when its third argument (for renderer) is null or undefined.