fix upper limits on how much can be rendered with the physics renderer
delete gl buffers at dtor (not that we use the dtors during the lifetime

of our game yet)
fix FTBFS from last commit, delete shader in tile renderer at dtor
del tilemap texture at dtor
cleanup tilerenderer unused vars
delete spritesheet textures
handle dtor for gui opengl renderer, destroy buffers
delete fbos and textures in various gl renderers

we don't *yet* destroy the renderers since disconnection isn't implemented,
but when we do, it should be for the most part, leak free. will have to
verify, obviously.