If FLAGS_calibrate_imu is set, would crash if inertial data was not supplied as updateimuweights was called.
use_only_when_static flag now vetted by calibrate_imu flag.
Fixes multi-camera display issue.
Adds some error reporting.
Adds small correction to log message.
Checks if the individual image timestamps are zero, and if so uses the device timestamp.
By recommendation of @chachi, restores the use of only_use_when_static flag even when there is no calibrate_imu.
Merge pull request #1 from arpg/fix/visual-only-calibration

Fix/visual only calibration