Created [Add a player] form

I start with the player management view, before the tournament starts. First thing, I add a player to the list of registered players.

TODO:
_immediate: Registered player management: editing, deleting, filtering, sorting
_later: known player management: adding (from implemented add form), add to tournament, editing, deleting, filtering, sorting, loading from <tom file>, export as <tom file>, save to local storage.