static/index-ls.html: Clear canvas before rendering; fixes flickering during play + drag
static/index-ls.html: Fix perspective, which was reversed before (bounding box rendering broken, fixed later)
static/index-ls.html: Rearrange mouse sensitivty and observer distance for more realistic setting - dragging feel should remain the same
static/index-ls.html: Darken bounding box with increasing depth
static/index-ls.html: Add support for optional perspective projection
static/index-ls.html: Fix the perspective correction - base it at the plane center instead of corner
static/index-ls.html: Put the bounding box by default around the whole image to help the brain's perception