AP_Scripting: add Plane autoland applet #1407

Job	Run time
build (base)	2m 14s
build-gcc-heli	2m 0s
build (clang)	2m 12s
autotest-heli (sitltest-heli)	10m 1s
autotest (sitltest-copter-tests1a)	7m 15s
autotest (sitltest-copter-tests1b)	9m 12s
autotest (sitltest-copter-tests1c)	11m 25s
autotest (sitltest-copter-tests1d)	8m 57s
autotest (sitltest-copter-tests1e)	9m 6s
autotest (sitltest-copter-tests2a)	8m 56s
autotest (sitltest-copter-tests2b)	28m 36s
	1h 39m 54s

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