GUI+REST improvements - yaml spec and advanced tab for entities

This adds some oft-requested functionality to the GUI and REST API:

* You can add children given a YAML spec
* Problem indicators are included in the summary reason when an entity is on-fire
* You can clear the problem indicators (so enrichers re-populate them if the problem recurs)
* You can see the blueprint YAML on the Summary tab
* You can rename an entity
* The REST API supports setting config and sensors (and policy config set has been fixed)

It also restructures the GUI (moving lifecycle, config, and some new things to the "Advanced" tab) and improves JSON rendering (using a Brooklyn-specific ObjectMapper).

Just use `.isEmpty()`