Better serialization detection

### Problem

When downloading a dump, it has to be streamed and analyzed. For reading it (after extracting it), the serialization has to be know. At the moment, the serialization is guessed based on the file name (https://github.com/dice-group/Squirrel/blob/master/src/main/java/org/aksw/simba/squirrel/fetcher/dump/DumpFetcher.java#L57-L72).

### Improvement

If the serialization is not known, we should have a class that starts to read the file and figure out which serialization has been used.

Start by reading src/main/java/org/aksw/simba/squirrel/fetcher/dump/DumpFetcher.java around lines 57-72, where serialization is currently guessed from the filename. Determine how an unknown serialization could be identified while reading an extracted dump. Done means files without a known serialization can be analyzed and read using the detected serialization.

Written by the indexing model from the issue text.