Decide where/how to store camera intrinsics

[marklescroart]

Need intrinsics for unwarping; unclear if we need a different intrinsic matrix for e.g. each separate t265, or whether it is safe to assume the intrinsics will all be similar enough for it not to matter.

[phausamann]

Pupil stores intrinsics in the recording folder if they have been estimated by the user (e.g. world.intrinsics for the world camera). I believe we need intrinsics for the FLIR camera as well as extrinsics between FLIR and T265 for each device. Good question whether T265 intrinsics are all similar, we should probably check with a couple of devices.