UCM: add option to identify positive coherence changes

[David-Loibl]

In the current concept, UCM detects only locations where coherence dropped from high to low values. However, it may also be interesting to detect locations where coherence substantially increased. For instance, material displaced by a rockfall event would lead to a substantial increase in coherence if deposited in a place where low coherence prevailed to this point, such as a forest.

This may be optionally activated in the config file. Increasing coherence may be indicated by negative values in the resulting file, so that UCM results would have a value range from -1 to +1.