Add functionality to deactivate buttons

[Deconimus]

Version of the game

current master branch

What is the enhancement?

Add functionality to deactivate buttons e.g. via a signal.

Additional context

See discussion in Pull Request #15 about deactivating buttons.

In Portal, buttons are deactivated on multiple occasions e.g. when an "escape hatch" cutscene was triggered. Visually, they will remain in their state before deactivation (pressed or unpressed) and they will ignore any further interaction.

Proposal

This could be implemented by adding a third optional argument to button objects in the blender files which is then listened to in the button update function. The new syntax for blender button objects would be:

@button <signal> <cubeSignal> <deactivateSignal>

[mwpenny]

Thanks.

For posterity:

Per discussion in #15 (comment), will hold off on this until more level object customization cases are known, so that we don't get overly-specific too early on.

For the time being, there is a workaround by ORing door-opening signals with their corresponding "escape hatch" signals, causing the former to have no effect after the latter is active.