updates to block implicit, matrix assembly (new test), and dual time integration needed for the reactor ensemble
- enable dual time integration with a nonuniform dual time step size
- add the 'ad hoc sens' test to cover four means of Jacobian assembly
- add dual time tolerance and a setter function
- changes to chain rule assembler and matrix mod, which are going to be overwritten by the new assembly abstraction we're working on
- make convergence check GPU-safe