bugfix to find correct event numbers when single tel file is read

Merged Moritz Huetten requested to merge bugfix_singlefilereading into master

Solve #3 (closed) and #4 (closed). Regarding #4 (closed), when a single MC file is read, all events are classified as "mono". Later stereo matching can be done by hand by the event_id. All real "mono" events no having a stereo partner, do have the event_id = 0 (as before).

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