Add additional Termination Criteria

[vvhof]

Currently, we can only terminate, if an additional solution is not found in a defined amount of instructions executed.

We should improve this to automatically terminate upon the algorithm reaching a predefined search-depths.

[timmaj]

Since iterative deepening is implemented, this should be an easy thing to implement. One additon configuration variable is needed. Then, when iteration until the predefined depths is finished and would restart check if iterativeDeepeningStartingDepth + iterativeDeepeningDeepnessIncrement is greater than the treshold and terminate if so. The more complicated option would be to exactly finish the treshold, i.e. if iterativeDeepeningStartingDepth + iterativeDeepeningDeepnessIncrement was less than the treshold but adding iterativeDeepeningDeepnessIncrement another time makes it to great, just add as much as to reach the treshold for the final run. Again, however, nothing needs to be changed to how Muggl works, it will be a couple of lines added to the core only.