Add plugin to edit probabilities at runtime

[eSoares]

^

[eSoares]

Instead of changing probabilities, maybe change scaling of them.
All probabilities start at scale 1, give possibility to scale them up (2 for doubling, 0 to disable rule).

Changing the scale makes it easy to respect multiple paths/events in a same plugin having different probabilities, and adapt them all at the same time but keeping the differentiation.

[eSoares]

Still it needs to exist a way to tweak multiple probabilities in a single plugin.