Cesium viewer sample

[GerardasB]

Changes

A sample application with the cesium viewer rendered in a frontstage which consists a few other UI items: widget, toolbar button, status bar item.
In this application IModelApp.startup and UiFramework.initialize are not called.

PR will not be merged as it serves as an POC around using the widget system w/o the IModelApp initialization.

Related Three.js viewer sample: #1119

Testing

N/A

[calebmshafer]

@GerardasB what do you think about making a true PR to add the capability to do this? Are there other gaps that we'd need to work through?

[GerardasB]

@GerardasB what do you think about making a true PR to add the capability to do this? Are there other gaps that we'd need to work through?

Sure, I'll need to polish this PR a bit and we can merge it in. I.e. ATM only a single point graphic/decorator that maps to a local iModel is rendered in a cesium viewer.