Extension: RTS-like unit selection

How To Use:

- The "Allow player to Select units" action must run every frame to work properly

- When a drag is in progress, all units inside the selection box will be "PreSelected"

- When the drag is released, all "PreSelected" units will be changed to "Selected"

- Hold the additive select key to add units to selection

- Hold the subtractive select key to remove units from selection

Control Group controls:

- Ctrl + (1,2,3,4,5,6,7,9,0) assigns that Control Group to Selected units

- (1,2,3,4,5,6,7,9,0) selects all units that are sssigned to that Control Group

Selection box:

- When dragging, the selection area will be drawn by a Shape Painter object. 

- If a Shape Painter instance has not been added in the scene, it will be created automatically.

- To change the appearance of the selection area, change the Shape Painter properties.

- Reduce the fill opacity of the SelectionBox (shape painter object) so that units and terrain can be seen behind it.

Tips:

- Use the "Preselected" and "Selected" conditions to highlight units that are being interacted with

- Create an object group (i.e. "SelectableUnits") to control which types of objects can be selected

- Use conditions to restrict which object instances can be selected. 

- Use the "SelectedUnitID" to design formations of units.

- Shape painter object should be on the same layer as the units being selected

- Always use ForEach() events when using the conditions in this extension because extension conditions do not currently perform object picking.