Better Oculus Rift blob tracking

[ricochet1k]

This PR has 2 commits that 2 contribute to better blob tracking:

• Better flicker tracking by storing area directly rather than counting arbitrary 10% up/down edges.
• Better blob tracking by associating each blob to the closest blob from the previous frame.

Also, fix 2 out of bounds writes causing crashes in gst. And not allocating extends for every scan line when they are never used elsewhere.