Kalman position estimation using linear Kalman filter with non constant gains
See INS_kf, contributed by @Spyroth in #332.
The filter showed improved performance compared to the complementary filter (Position_estimation). It estimated accelerometer biases, it also estimates altitude (vs origin) and height (vs ground) independently.
Refactoring of Waypoint handler, Mission planner, Navigation and controllers
by @mdouglas90 and @basil-huber in #331
Synchronisation of waypoint list is separated from navigation logic.
Waypoints are treated differenlty based on the attached MAVlink command.
A mission handlers registry was added, it contains a list of mission handlers. Each mission handler can treat specific mission items. For safety, a mission is accept only all its waypoints can be handled.
This architecture also makes it easy to add new behaviour for a new MAVlink command by simply adding a new handler to the handler registry.