Scripted element properties encoding scripted element IDs get mangled

[LBPHacker]

The solution is to extend the element palette mechanism to particle properties that are known to encode element IDs. New element properties or Properties flags would be introduced for annotating such particle properties, e.g. PROP_CTYPEELEM and PROP_TMPELEM.

[simtr]

This would also be useful for the HUD in the top right to only display ctype elements when it's used for element storage, and could apply to builtin element types too, to simplify the HUD code.