Changes to mcl_burning.set_on_fire():
* Add logic that only updates the burn time, but skips adding fire
entities to objects that are already burning.
* Condense code a little, remove single use variables.
* Add a comment to a questionable piece of code.
* Add comments to the function.
* Add update_hud() function.
* Remove the client channels.
* Unglobalize animation_frames variable.
* Fix bug where player state was not stored on shutdown of singleplayer
game.
* Remove superfluous sanity_check() function, this code could easily be
inlined in its only caller.
- Use upright_sprite for 3rd person flame display, which is both closer to minecraft and allows for client side texture animation
- Take care of flame HUD in the MineClone2Client
