Copter: replace quad trapezoid frame with V

Also update motor mixing
Copter: fix THR_ALT_P documentation
Plane: update GCS_Mavlink parameter documentation
Copter: make guided mode start at current location
Copter: remove noise and wind from copter sim

this is to help Randy track down a current problem
Copter: adjust trapezoidal motor mixing
autotest: allow testing of elevon planes

this fakes up an elevon plane using the Rascal110
Update AP_MotorsOctaQuad.cpp

There were two "4"s in the motor test order values. Presumably a typo.
autotest: added link for QUpgrader to web-firmware/index.html
AP_InertialNav: use shared GRAVITY_MSS constant
autotest: added support for vtail testing in runsim

virtual vtail support
Plane: added VTAIL_OUTPUT option

this allows for software vtail mixing
Plane: fixed failsafe with VTAIL_OUTPUT
Copter: Jason's bug fix for loiter's set_next_WP_latlon
Plane: simplify the VTail mixer to be more like a hardware mixer

this should make it easier to trim the vtail
Plane: expand the VTAIL_OUTPUT docs for APM1
Plane: copy rudder out in TRAINING mode

we were doing rudder mixing in training mode, which shouldn't be done
Copter: reduce compiler warnings
Copter: remove #ifdef checks for Atmega1280
INS: switch to global definition of GRAVITY_MSS

saves 4 bytes of RAM