+ Appeared if .Integrate(..., relax=True) used after an external field was applied earlier.
  + Computation was already correct before.

+ is done in fixpoint loop anyhow

+ already done within self._StepPrepareWithoutTaskManager()

+ it's already computed in self._StepPrepareWithoutTaskManager()
+ it's time independent

+ already assembled in self._StepPrepareWithTaskManager()

+ use m / |m| for building Q[m]

+ Should fix problems with bem++
+ to be tested with sp4

+ always treat hc as f
+ --> this means hc_mp ~ hc(t+k/2)
+ --> and hc_impl ~ hc(t+theta*k)