Following the discussion in #173, the integrate_const function now
provide a mechanisms to check for TOO_MUCH_WORK situations where too
many steps are performed without any progress (i.e. observer calls).
Naturally, this only makes sense for controlled steppers or dense
output steppers.
Also, integrate_adaptive functions do not require such functionality as
there observer calls happen at every time step.
Hence, only integrate_n_steps and integrate_times will be adapted shortly
