v1.7

Changes

• Fix orientation in backend_light
• New dummy backend for testing
• Fix and improve aeroarms model
• Add new model aeroarms_pendulum
• Expose UAL state (#9)
• Add argument to expand gazebo model path
• Force UAL state when calling recover from manual
• Force land to override any previous flying function
• Add set home function to UAL
• Prepare test_server.launch for other px4 modes
• Reduce queue size for mavros topics
• Fix orientation bug in example test
• Force disarm after land, as it failed in real uavs