Mission waypoint update

[guiccbr]

The current mission waypoint is taking too long to be updated, specially right after takeoff. This makes the vehicle rotate to the home position while already moving to the next mission waypoint, what is a big problem since it might cause the vehicle to be moving in a given direction facing backwards.

[guiccbr]

Fixed in PR #10

[guiccbr]

PR #10 successfully prevents the vehicle to auto-rotate in the direction of an outdated mission waypoint. However, the mission waypoint update delay still can be observed, what causes the vehicle to move back to the home position for some seconds right after takeoff. We need to take a closer look into this issue in order to fix that problem.

Possible roots of the problem:

• MISSION_CURRENT mavlink message broadcast sample rate might be too low.
• for some reason mavlink_vehicle::is_ready() might return true before the initial mission waypoint has been received.