Copter: reduce alt hold defaults

Throttle Rate P to 5.0 (was 6.0)
Throttle Accel P to 0.5 (was 0.75)
Throttle Accel I to 1.0 (was 1.5)
Frame_Params: Added 3DR Iris+
TradHeli: update AttControl params to match multicopters
Copter: increase EKF_CHECK_THRESH default to 0.8

Also remove unused #define related to inertial nav check (now removed)
Initial Commit
CHDK-Scripts: adding README.md
CHDK-Scripts: Adding kap_uav
DataFlash: allow use of a smaller writebuf for PX4v1

this fixes logging on PX4v1
Frame_params: Updated 3DR_Iris+.param
Copter: send extended status to GCS only after initialisation
Copter: never send unhealthy terrain status

Copter does not yet rely on the terrain data (it's for informational
purposes only) so we will temporarily disable the failure flags to the
GCS to avoid support calls
Copter: arming check that throttle is low
CHDK-Scripts: Preparing to replace the script files
Copter: Parameters.pde
Corrected typo in parameter description
Frame_params: 3DR_Iris+.parm
Plane: improve the short and long failsafe docs

thanks to Mark Jacobsen for the analysis!
CHDK-Scripts : initial commit
CHDK-Scripts : add instructions
Frame_params: Removed Iris with 3 Position Mode Switch.param