Demand Queries for Generic Domains

[beyeler]

This PR adds full support for generic domains in PySats including demand queries. When creating an instance of MRVM or SRVM you may set the "generic" parameter to true to create a generic domain (analogous to the original SATS).

The generic model provides the same functionality as the PySats SimpleModel by representing a bundle as an array of integers instead of an array of {0,1}. Additionally, it provides the following functions and properties:

• licence_to_good: dictionary that maps each licence id of the non-generic model to the id of the generic good. This allows to transform a bundle from a non-generic model into a generic model bundle.
• good_to_licence: dictionary that maps each good id to the corresponding lists of non-generic licences. This allows to transform a bundle from a generic model into a non-geric model bundle.
• get_capacities() dictionary that maps each good it to the corresponding supplied quantity of this good