Add a HMD MultiSelect button
Since it's impossible in HDM to do a multiple selection
This adds a MultiSelect button (available in HMD only)
When active, the selection in the list behaves like having CTRL pressed
When inactive (default value) the selection in the list behaves as before (on item only)
This adds the support for 6 new buttons:
Copy-Cut-Paste-Duplicate-Undo-Redo
It adds the automatic toggling of the HMD only buttons:
Copy-Cut-Paste-Duplicate
