Copter: double flash arming light when pre-arm checks fail

Hardly my finest work but it's temporary because we're going to replace
all the led, buzzer etc with a library called AP_Notify in the near
future.
ACMotors: bug fix to yaw limit
Copter: yaw limit fix to allow I to reduce

We now allow the I term even if we've hit the yaw limits as long as
updating the I term will reduce it
Copter: reduce default Loiter Pos P to 0.2 (was 1.0)
WPNav: reduce default WP_ACCEL and LOITER_SPEED
Copter: relax pre-arm checks for mag field

previously it was 50% ~ 150% of expected mag field but now expanded to
35% ~ 165%.
Copter: roll-pitch fix to allow I to reduce

Contributed by Leonard Hall
WPNav: reduce loiter speed used to correct pos error

Contributed by Leonard Hall
This should reduce the aggressiveness of the response when we experience
a GPS glitch
Copter: change firmware version to 3.0.1-rc2
WPNav: rounding error fix in loiter

Contributed by Leonard Hall
WPNav: bug fix to loiter accel calculation

Contribution from Leonard Hall
WPNav: bug fix to reported distance to target

This value is for reporting purposes only
WPNav: replace LOITER_ACCEL_MAX with parameter

Also removed unused _lean_angle_max variable
Copter: update release notes
Copter: typo in release notes
Copter: default Loiter Pos P to 0.8 (was 0.2)
WPNav: stopping point projection uses wp_leash
Copter: project stopping point for loiter command
Copter: increase Yaw Rate I 0.02
Copter: revert Loiter Pos P to 1.0 (was 0.8)