Consider the possibility of using a TreeGrid instead of Grid

[mlopezFC]

A user mentioned in the directory about the possibility of using a TreeGrid instead of a Grid.
I think that there are three different ways of using a TreeGrid:

1. As a replacement for the left grid: In this case it would be like a better way of "classifying" the items that can be added to the collection. So instead of having a filtered grid, we could organize the available items in branches of the tree, so we could handle a lot of items in a better way. This is the simpler choice, given that we would still create a list of selected items.
2. As a replacement for both grids, but "respecting" the hierarchy. That means that if we add a node from the left, it would create all of the parents in the right grid. This is a more difficult strategy, because instead of a List we would produce a Tree. But at least the handling of the items would be not so difficult because the produced tree would be a stripped down version of the left tree.
3. As a replacement for both grid, but allowing to create a different tree in the right. This would be the more difficult strategy because it would allow to create a complete different tree.

[paodb]

From Moritz Christian on directory:

Thanks for being interested in the idea. Typically the hierarchy shouldn't change in those kind of scenarios, so each item on either side has the same parents. The component should offer the possibility to add a whole subtree including children or just one item (leaf) at once, whereby the necessary parent items would be created automatically.

[mlopezFC]

The following:

The component should offer the possibility to add a whole subtree including children or just one item (leaf) at once, whereby the necessary parent items would be created automatically.

Should be handled by the selected item on the left. If the selected item is a subbranch, then all of the children (and the necessary parents) are going to be created on the right.
If only a leaf was selected, then only the necessary parents are going to be created, and if the root node is selected then the whole tree is going to be transported to the right.
In the oposite direction, if a leaf is selected, then only that one is going to be "removed", but if we select the root node, then the entire tree is going to be removed.
In this approach, we need to find a way for marking the parts of the tree that were copied to the right, because I don't know if removing them would end up in a nightmare when trying to re-create it if the are already selected values.

[javier-godoy]

This feature requires the enhancement proposed by #96 (in addition to the other changes that @mlopezFC mentioned above)

[javier-godoy]

Moving back to triage to clarify the feature's requirements.