Added percentages to stats.

Added percentages when stats are outputted. Updated output for
"gamestats" command when no parameter is given.
Refactored some stats code.

Made update_roles_stats() and update_game_stats() a bit cleaner.
Added check for abnormal game stop before updating game stats.
Added get_player_totals(). Some code cleanup.

If the "player" or "mystats" command is called without a role,
then the bot will now list the total games that the player has
played in each role.