Window / Dialog component - replaces direct use of Blueprint dialog

[amcclain]

We make frequent and direct use of the Blueprint Dialog out of kit. There are some concrete issues with this:

• In general we want to avoid needing to go into kit for core components, as it reduces our flexibility to swap out third-party library comps for alternate implementations.
• Can't use these same components cross-platform.
• BP dialogs make use of inner header/footer components / classes which I find somewhat ambiguous (are they required? do we use them consistently?) and have some styling / sizing differences from our other comps (namely toolbars and Panel headers).
• No support moving / resizing / maximizing.

We could consider:

• Lightweight wrapper around Dialog to avoid the kit imports, or...
• Wholesale replacement of Dialog - could be done via addition of floating / positioned support to Panel.