initial commit of Velvet Generation support script

[richranallo]

This is a support script for Velvet Generation, enabling some of the weird stuff we need to do with dice in that system. As the description says, it does the following:

• makes all d6 dice dragged onto the table from chat controllable by all players (players need to move dice around the tabletop, even if they were rolled by others).
• adds a command for !amped, which acts on all selected dice tokens and rerolls any that are set to 1, with a visual effect to indicate it.
• adds a command for onFire|* which acts on all selected dice tokens and sets all 1s to the number indicated by *, with a visual effect to indicate it.