UI/Input/Container: add JS to retrieve values clientside

[nhaagen]

This adds some JS to the UI Form to retrieve its values client side. The JS builds an internal tree over the container's elements by their names rather than their position in the DOM. Consumers may search for a FormNode and retrieve values from all elements below. Optional or Switchable Groups will only relay values if selected.

Please note that this is a basic addition without any visible effect, yet, but it will be very handy in folding forms/groups/filters and visualize current selections of otherwise invisible inputs.