* Changed sitl_gazebo to the advanced liftdrag plugin fork.
* Added advanced plane and its associated parameters to PX4. Also tweaked one of the plugins to fix a compilation error (upcasting from float to double).
* Switched gazebo back to main branch, to avoid merge conflicts.
* Change simulator bridge back to what it was in main branch
* Changed sitl_gazebo to match the PX4 main branch's (commit hash b968405)
* Changed SimulatorIgnitionBridge to match most recent main.
