Feature: Enable counter effects

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Some effects may be necessary to implement as counters, e.g. if a monster applies a stacking damage bonus or something. Or if the user wants to use effects to track uses of a spell that has limited spells.

Currently the only way to do this is to add multiple effects, but it could be done in a way that we add a counter to effects, and the player could easily increase the counter on the new Effect Panel by clicking on an Effect, or decreasing it if right-clicking (ultimately deleting the item that proves the effect when the effect counter reaches 0).

Since there are no items in the Quickstarter written like this RAW, I'm not doing this as part of the Effect Overhaul (Tracked in #276).