Format filenames as plain text.
Update the action bar player spinner when players change.

- Call any onPlayerChanged callbacks when the list of players changes.

- Update the Player model to record the connected state of a player.

- Change updatePlayerDropDown to only include players that are connected,
  and only show the spinner if more than one player is connected.
Reformat model/Player.java.

- Keep fields together, ordered, and named consistently.

- Move the constructors to the top.