Fixed a synchronization problem that was allowing unconverted images to
be returned
Added helper function to truncate an x,y position to an image shape
Got most of the crashing fixed by skipping templates with zero size and
truncating templates to within the image frame
subscribers.py: new class for capturing ardrone navdata output
flownav.launch: set default parameters for looprate and realtime
common.py: added some convenience functions
flownav.py: added a small cli which includes option for playing from bag
file. Added navdata capture.