Allow reading JSON CASes with out-of-order SofaFSes

[reckart]

Describe the bug
Although the JSON CAS 0.4.0 specification says that SofaFSes need to come before any FSes referencing them, the Java implementation does currently not enforce this. However, the Python implementation currently relies on this.

Expected behavior
Best, the Python implementation should be changed to support loading JSON CASes with out-of-order SofaFS for reasons of compatibility and usability.

Please complete the following information:

• Version: 0.7.5