mavlink: commands stream implemented
Revert "Merge pull request #816 from PX4/mavlink_commandlongstream"

This reverts commit 00ef10f307d3c4a262a15ab5747d854eb4c568d5, reversing
changes made to d55e64d1e54542762510387a22897f504c68a5a6.
Merge branch 'mavlink_command' of github.com:PX4/Firmware