Refactor "cooldown" `deque`s and associated logic into a common class

[ZeroKnight]

The concept of a "cooldown" deque for various ZeroBot phrases is common enough in the current set of feature modules to warrant them and their associated logic (e.g. _resize_*deque) to be encapsulated into a class in ZeroBot.common.

Ideas

• Constructor can take a (reference?) config key that determines the cooldown (i.e. the deque size)
• Should extend deque using the appropriate class, similar to UserDict
  • We'll need to compose a deque since we'll be resizing them, which requires a copy.
• Handle cooldown count changes
• Integrate with #24

[ZeroKnight]

Deciding to scrap this idea. There's very little "boilerplate" common enough between features (currently) that would warrant the overhead of a class, not to mention that how each module may use its cooldown deque will likely vary enough to cause using any implementation to be rigid and awkward.