Fix calculation of probability of root fault in FTA

[kostobog]

Calculation of probability of FTA events does not consider that some of the events in the FTA are the same event, i.e. there are events in the tree which are not independent.

To fix this use an existing library (https://github.com/mbarrere/mpmcs4fta) to calculate probability in a fault tree.

[kostobog]

Here is an example where the current computation may go wrong. The first diagram shows a causal graph (not an FTA) to depict the common event that can cause different fault events.

The second diagram shows the FTA of the causal graph from the diagram above