Feat: add grouped ilk emergency spells

[amusingaxl]

I decided to remove the hard-coded ilks approach in favor of a more general one which allows us to specify the desired ilks in the constructor.

Regular spells are executed through a delegatecall from MCD_PAUSE_PROXY. For that reason, they usually should not have storage variables, as they'd be accessing and interacting with MCD_PAUSE_PROXY's storage, not their own.

However, Emergency Spells are not required to interact with MCD_PAUSE and MCD_PAUSE_PROXY at all. They execute actions through regular call on Mom contracts, so we don't have this limitation.

Even if the contract is somehow misused and used as a regular spell, interacting with MCD_PAUSE, there wouldn't be a problem because the storage cannot be changed outside the constructor.

This approach requires some amount of hacking due to some Solidity limitations (i.e.: no support for immutable arrays, bytes32 <-> string conversion shenanigans).

While there is still some code duplication, this is significantly reduced compared to the previous approach.

[amusingaxl]

Technically, nothing prevents us from setting MIN_ILKS = 1 and replacing the single-ilk spells with this one. We'd just need to pass a list containing 1 single ilk to the constructor.