TECS : Initial implementation of TECS (Total Energy Control System) for integrated speed and height control

See pull request #260 for details
Plane : APM_control : Modified gain definitions for roll and pitch controllers so PID gains behave like previous servo PIDS

Gain definitions in roll and pitch controllers were updated previously so that the old PID tuning values could be transferred across.
Updated tuning guide for revised gain definition.
TECS-WIP : Changed default damping gain
Default damping gain was changed from 0.0 to 0.5. Results from flight testing indicated that baro delays were larger than modelled, requiring some damping gain. This default value will be refined with further flight testing on a range of models.
PX4 : Dirty hack to fix channel order difference when using SPektrum radio via S-BUS
Plane : Elevon Output Mixer : Removed /2 so that both channels can access full deflection individually
Hack : Temporary pitot source pin reassignment
TECS-WIP : Added compensation for additional induced drag in turns.

Also updated default parameter values based on SITL and flight test results.
Also fixed typos in comments
Plane: allow selection of TECS at runtime

set ALT_CONTROL_ALG=2
TECS-WIP : Removed printf and added debug statement
TECS-WIP : Height filtering improvements
TECS-WIP : Added adjustable weight for spdvs height control
TECS-WIP : Added hard limit to pitch demand integrator state
TECS-WIP : Added individual damping gains for pitch and throttle loops
TECS-WIP : Fixed Arduino compile error
TECS-WIP : Modified default pitch demand damping gain value
TECS-WIP : attempt at logging tecs data
SpdHgtControl: support logging of internal tuning data
AP_TECS: added logging of internal tuning data
Plane: call out to TECS logging function