Improved update_coords
BD init code was being checked for every integrator at every step, and
BD and SD init code was being run for every step of those integrators,
so moved that to update_temperature_constants (and called it from
init_update). The reference temperatures for coupling could change
under simulated annealing, so updated that code to call the new
routine.
Used gt as the temperature-coupling-group iteration variable, rather
than n (which is often used in the update code for a per-atom index).
Reduced the scope of some variables in init_stochd.
Added some const correctness for inputrec.
Change-Id: I8da3da018157c6834c2ca04abc65ba6b55a0fe98