conception/update #93

This branch updated the old documentation.
I made an architecture diagram for the web application.
I also added a new markdomwn "Description.md" containing all class diagram and a brand new description for each of them.
Please in future update the documentation of the conception each time you change something because we are going to be marked on sunday the 21st.

 In general, we use the implementation "SimpleFunctionValidator".
 We reconize the strategy pattern. Indeed, we need a family of algorithms because we have many classes that only differ by the way they validate.
 Futhermore, you may have notices the ComposedValidator that allows to chain several Validator.
 We naturally used the composite pattern to solve this problem.

 Now, let's discuss a much bigger part of the diagram.
 In this part we find all the team logic. Actually, a team only have an array of members and a "TeamInfo".
 The class "TeamInfo" exist to allows to split the data of the members.

 ## Session's class diagram
 ![Session's class diagram](./assets/session.svg)
 It encapsulates the PHP's array "$_SESSION" and kind of replaces it. With two interfaces that dictate how a session should be handled, and same for a mutable one.

conception/update #93

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