Add boolean simplifications

[Boyan-MILANOV]

This PR adds the following simplification patterns on constraints that we often encounter within MATE:

!(a||b) -> !a && !b
!(a&&b) -> !a || !b
a == True -> a
a == False -> !a
1*a -> a

[Boyan-MILANOV]

Ready for review now. I've added tests for all new simplifications. The additions are minimal despite the long commit history.

[ekilmer]

Few small nits but otherwise LGTM!