Core: improve config loading (in particular IO_System_From_Config)

[GPMueller]

The IO_System_From_Config API function should be improved by either logging cases that are not supported or by adding support for them:

• if (chain->images[i]->nos != system->nos) return 0; should change the geometry for the chain or log that it cannot be changed for a single system
• if (chain->images[i]->hamiltonian->Name() != system->hamiltonian->Name()) return 0; should change the Hamiltonian of the chain or log that it cannot be changed for an individual image

Note: the chain should probably not be changed by IO_System_From_Config. Instead, one could add IO_Chain_From_Config.

[GPMueller]

As noted in #528, it would make sense to allow the user to specify whether the geometry should potentially be updated when reading images/chains.