Give theorems names in simpsets

This is to allow them to be removed easily. System builds on -t1, but
there are still two things to be done

1. the names associated with export_rewrites calls aren't passed on to
the simpsets yet
2. there is not yet an API for removing them

Also, perhaps just as an interim measure, I removed the unused
entrypoint for removing rewrites by pattern matching against their
LHSes (simpLib.remove_theorems).

Move pair, one, sum and option into one combined coretypes directory