Base for the exos.
Exo 1: create a model, save it, and fetch it.
Exo 2 : create a view associated to a model, and display it.
Exo 3 : communication between a view and its model.
Exo 4: create a collection, and display it.
Exo 5 : fetch a collection and display it.
Exo 6 : create a new company, and add it to the collection.
Complete

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