Event fingerprints and comparison

[rakow]

The EventsUtils.compareEventsFiles method is often used within tests to check if a simulation result is still as expected or if there is a potential regression.

However, when testing a full scenario, the generated event files can already so big that they should not be checked into git.
Simply storing and comparing the hash of an event file will often times not be sufficient, because event files could be semantically the same, but produce slightly different event files. For example, events at the same time step can occur in any order, as well as attributes within an event.

For this reason, this PR introduces an event fingerprint file format, which contains very reduced information of an event file, but still allows for checking the same type of differences that the full event comparison will return. I.e. different timestamps, different number of events, etc.
In our test scenario, a ~16MB compressed event files results in a ~120kb compressed fingerprint file.

The new functionality should be used via EventsUtils.createAndCompareEventsFingerprint or EventsUtils.assertEqualEventsFingerprint

Also, many thanks to @zlukich for helping with the implementation.