Updating step size control

This PR changes the step-size control for LMMs and revises the way the step-size is updated at each step for RK methods.

There is still some work currently in process to make the code more efficient and robust.

Note there is a test that fails in parallel (acoustics_2d_homogeneous) when SSPLMM32 is used, but could not reproduce that in my machine (where all tests pass).
I think this method is identical to that of the parent function, so there is no need to explicitly duplicate it here.  It will be automatically inherited.