Use ReadQueue for PhotonCamera timestamps

[mcm001]

This removes the extra GetLastChange call to keep everything properly atomic.

Closes #1303

[srimanachanta]

What's the overhead of enabling poll storage? If it's somewhat decent we should make this a configurable option when actually creating the camera.

[mcm001]

It just makes the circular buffer of std vectors of bytes larger. Since the contents of the vector are dynamically allocated, the cost is zero, and then as you push more new packets in, you allocate new memory. So probably on the order of 20kb, at worst, of dynamically allocated memory, and 20*sizeof(vector) statically?