Standardize example format

[jardinetsouffleton]

As of now, all examples follow slightly different logics in the way they declare and organize:

• agents
• variable selection
• value selection
• utilities
• featurization

To make adoption of SeaPearl easier, we should design a simpler, streamlined way to create an experiment. This process should start by trying to develop a unified process to define an experiment and could eventually lead to a high-level wrapper inside SeaPearl.