Flyout getMetrics causes a reflow and style recalculation

[picklesrus]

Very similar issue to what a67f841 solved.

Extra considerations for the flyout:

• Flyout also contains labels and buttons which need to be added to the bounding box calculations.
• Gaps as specified by the toolbox/flyout xml.

[alschmiedt]

The flyout now stores its width and height every time reflow is called. The metrics manager uses these values every time we call getMetrics instead of calling getBBox on the html div.