Improve how dates are handled

[banool]

Currently the program pre-generates all of the necessary dates into some kind of list (I'm not 100% sure honestly). The code chunk (it's not even a function) which does this has all manner of duplicate code. It'd be nice to streamline this.

For starters, the code which determines which weeks we want to generate needs to be totally split from the code which populates this date list. There are further abstractions no doubt which could make this more pleasant.