Using prototypes and inheritance like a boss

I used inheritance for all different age groups available.
Meanwhile, I also created objects to manipulate player lists more easily. This means less direct DOM manipulations and a clearer code for the future.

TODO:
_required: update the last form's view accordingly
_required: use the last set of rules to update the last form's view behavior
_optional: add filtering support to the view (currently available in the code but unused)
_optional: manage edition and deletion of a player
_optional: adapt export accordingly
_optional: look at current xml for players in tournament files, to see if it is the same structure as in a players.xml file. If yes, start some import and export methods inside the PlayersList object.