Simplify the system that reactively triggers realizations, at the cost
of removing the preconditioning step described in issue #101 and doing
unnecessary realizations after certain kinds of updates.
The new system should trigger a realization after any update that could
affect the assembly's deformation space. For simplicity, any update to
the regulator list triggers an update, even if it doesn't affect the set
of constraints. In particular, adding a regulator triggers an
unnecessary realization.
