See merge request !9

`setLog` must be used by the program using the library to define which logs
should be published.

Stop using a custom logger for subscriber.
When drone logs are required during execution (a.k.a debug mode), they are now
send through OPC-UA.

See merge request !8

Checking for landing is used for a security purpose. If landing procedure is
triggered but not by the swarm management script, it means it has been triggered
externally most probably for emergency reason.

Define the number of OPC-UA variables of each entity (drone or subscriber) in a
global value.

Use an integer type to keep integrity of the data coming from the autopilot

Include timestamp into position array

Return a position object instead of using various getters.

Add latitude, longitude and altitude parameters to loiter function as this
functionality is required to land safely.

Included changes are required to use the autopilot's version complatible with
mavlink 2

See merge request !7

Rather than using manual control and therefore losing benefits of the autopilot,
setTargetCoordinates now uses doReposition but with GPS coordinates 200 meters
further away (2 times default radius) than given coordinates.

See merge request !6

Merge subscribeOnly function into runPubsub

Add to published variables an array composed of the yaw angle of the the drone, its airspeed and its climb rate.

Send a position array instead of multiple variables