bunch of stuff

-added origin point to animation manager (can be accessed through
function on individual ST_Sprites)
-rotatin bullets
-added draw() to ST_Sprite
-blocked update and draw on inactive stuff
-bullets outside screen/too old get killed
-minor animation update
various fixes and improvements

-abstracted integration so that you can just multiply by STI.corrector
instead of having to recalculate the factor every time its used. Less
expensive and easier to remember this way
-corrected animation class stuff so that it's also based on the
deltaTime instead of an integer counter (makes the animations skip
frames when necessary in order to catch up to current time and
accumulates time to avoid getting offset during framerate drops)
-got rid of the old bulletmanager we never used
-added generic deactivate() and reactivate() for detachment recycling
-replaced "/2"s with "*0.5"s