(minor) Add support for disabling redrawing when removing objects

All 'remove' methods will now accept a redraw parameter, both to
match the API for all 'add' methods, and to allow removal of
objects without redrawing (good for removal of many objects at
the same time).
When un/loading a scene, redraw canvas only once, instead of per object
Merge pull request #93 from joelpurra/scene-redraw

When un/loading a scene, redraw canvas only once, instead of per object
Update version to 2.6.0