Switch away from NI interrupt manager to custom implementation

[ThadHouse]

The NI implementation doesn't allow us to dynamically change the mask without an allocation. However, there are reasons to want to do this, especially for reading multiple interrupts, so changing to a custom implementation is easy and solves the problem.

Still needs a bunch of testing, just didn't want to lose the commit.

[Starlight220]

This doesn't have any user-facing changes, right?

[ThadHouse]

Nope. It will allow a new user facing api in the future, but existing things stay fine.

[ThadHouse]

/wpiformat