AIS: cater for multiple parallel configurations

[CarstenWickner]

As an AIS user I want to be able to configure multiple different models of assignable categories in order to work with different approaches on multiple projects in parallel.

The AIS module already allows for the assignable categories to be freely configured and stored as part of the respective project file. However, only a single version of the model is being stored at any time and is being applied to any new project.
Instead, users should be able to configure multiple models and be asked which one to apply when starting a new project.

The configuration could look similar to the configuration of syntactic functions per origin language in the HermeneutiX module.