[Beta] Improve the drop down with the tree of components

[stefano.menci]

1. Make the drop down longer, so there is no need to scroll up and down
2. Make is a pinnable/collapsable panel instead of a drop down, so it is possible to see if the component being dropped did actually drop inside the intended container
3. Make it a tree with collapsible nodes, so it is possible to quickly see all the containers and only expand the desired ones
4. Make each node draggable, as already requested here

In some cases dragging a component inside a container on the tree rather than on the graphic form editor may not be enough. For example dragging a button inside a DataRowPanel wouldn’t know what column to use for the dropped component. A solution could be to add one child per column, so one would drop the component in the column place-holder child of the DataRowPanel instead of the DataRowPanel itself.

[p.colbert]

@stefano.menci

A solution could be to add one child per column, so one would drop the component in the column place-holder child of the DataRowPanel instead of the DataRowPanel itself.

What a practical idea!