[Scenario-Reader] Force same behavior for reading vadere projects and single scenario files

Current behavior

The static methods in IOVadere are used to read in Vadere projects and the scenario files they contain.

1 vadere project

If a Vadere project is opened in the Vadere gui, the scenario files are migrated for the first time in the IOVadere class. This ensures that the read jsons can be deseralized. In a second step, the scenario files are actually migrated.

2 single scenario file

If Vadere is controlled via Traci, only one scenario file has to be read in. During the read-in itself, no migration is performed, which may cause the deseralization to fail. If deserealization is possible, the actual migration takes place in step two.

Problem

Due to the missing migration in 2, the deserialization can fail.

Goal

same behavior for 1 and 2

Procedure

I added the migration to 1