Design flexible event system that can replace the global SECTION_TIMES

[schmoelder]

Currently, all sections are global, however, for advanced systems, it is advantageous to only define events per unit operation.

E.g. it is difficult to design processes that simultaneously use gradients, non-constant input profiles, and have complicated switching procedures in the system. This is especially true for optimization because the "parameter path" can change if the order of events switches.