Update submodule ecl to latest Tue Jun 18 20:37:33 EDT 2019

    - ecl in PX4/Firmware (4673dd0): PX4/PX4-ECL@0f49eb3
    - ecl current upstream: PX4/PX4-ECL@a036cf8
    - Changes: PX4/PX4-ECL@0f49eb3...a036cf8

    a036cf8 2019-06-14 Paul Riseborough - EKF: Remove use of of quaternion self product operator and fix delta rotation sign
0e946f2 2019-06-14 Paul Riseborough - EKF: Remove use of quaternion self product operator and fix delta rotation sign error
ad7f7af 2019-05-21 CarlOlsson - ekf: correct quaternion multiplication order
d6351bd 2019-05-21 CarlOlsson - EKF: update comment
7612fa4 2019-05-30 Paul Riseborough - EKF: Don't start using GPS for height until all validity checks have passed
cef2ba5 2019-05-08 Roman - implemented Kahan summation algorithm for adding process noise to delta angle- and delta velocity bias variance