adding APM and Flysky FS-I6 compatibility

[tednv]

ok, i think i have it sorted out now, i spent a long time trying to get this to work a few weeks ago but now my frame is in pieces so i cannot test but this is what i had working in missionplanner. readRX() should not be updated because the last channel (10 which is actually 11) does not get used for ppm output, it is only there to shift the pwm mapped gimbal channels up

this version of the code allows for the original configuration with overrides for stuff i tested with apm mission planner

i will retest it again this weekend if i have some time to put my 450 frame back together

[tednv]

just retested this exact code with APM + Mission planner

to use, change APMTarget to true and uncomment the three lines below