Improve configuration of clingo via the API

[MaxOstrowski]

• Currently there is no way to detect if the program was startet with --text in the API.
• It would be nice if the configuration file would also handle options added by the user via the API.

[rkaminsk]

I am not sure what is the best way to add this to the API. One way could be to extend the configuration with (possible read-only) values. I am not sure how difficult it would be to implement this in the existing system. This solution would have the charm that this is an often requested feature.

[MaxOstrowski]

It would be nice to be able to use the portfolio feature (--configuration=file) to also parse options added via the clingo API.