capture from first camera

(We really need a better way to manage which device we're
capturing from...)
capture from first camera, here too
port try_exposures to c++

(does not work reliable on beagle if we set exposure from python
and then capture using CaptureOneFrame...)
remove failed experiments about setting camera exposure
try capturing multiple frames for each exposure
don't reset exposure for every frame

(On the beagle, the issue seems to be that the change in exposure
takes place after a while, so we need to wait a few frames before
it takes effect.)
Merge branch 'master' of github.com:cberzan/drones-287
hardcode exposure everywhere, for now
some images for the presentation
fix conceptual error in pose estimation
explain pose estimation
Merge branch 'master' of github.com:cberzan/drones-287