Implement usage of external OSI

[TimmRuppert]

Describe the feature

Within the CMakeLists.txt we have a parameter called USE_EXTERNAL_OSI.

This parameter currently does nothing (or to be more precise throws an error). We need to implement the usage of an external OSI library in order to be able to use the asam-osi-utilities more efficiently in external projects (e.g. gt-ge-core or openMSL). The current implementation would require multiple OSI instances.