Add support for tacking/reading scrollbar position in ContentPane

This patch adds a visual property "scrollcaptureEnabled" for the
ContentPane component defaulting to false. If enabled the
component tracks all scroll modifications and writes them back
into the pre-existing component properties.
Input value peer mapping and property delegation for scrollposition properties.
Merge branch 'feature/scrollcapture'

Conflicts:
	src/client/testapp-interactive/TestApp.js