Replace ogs5 IC/BC, process types with 'process variable'-centric approach.

This is used the [CommandLineApplication](https://github.com/endJunction/ogs/tree/CommandLineApplication) branch.

This pull request is providing basic ideas for further development. There is not much which can be accomplished with this data structures so far but reading in configuration files (see this [gist](https://gist.github.com/endJunction/e42f2e57c111d30d3e67)).

@rinkk As mentioned in the discussion this breaks the data explorer. Maybe it is a good point for freezing it.