AC_AttControl: adjust default rate IMAX and Yaw Filt

Increase Roll, Pitch and Yaw IMAX from 0.444 or 0.222 to 0.5
Decrease Yaw Filter from 5hz to 2.5hz based on the results of autotunes on many vehicles which always seems to produce values between 2 and 3hz

libraries/AC_AttitudeControl/AC_AttitudeControl_Multi.h

@@ -17,7 +17,7 @@
   # define AC_ATC_MULTI_RATE_RP_D           0.0036f
 #endif
 #ifndef AC_ATC_MULTI_RATE_RP_IMAX
- # define AC_ATC_MULTI_RATE_RP_IMAX         0.444f
+ # define AC_ATC_MULTI_RATE_RP_IMAX         0.5f
 #endif
 #ifndef AC_ATC_MULTI_RATE_RP_FILT_HZ
  # define AC_ATC_MULTI_RATE_RP_FILT_HZ      20.0f
@@ -32,10 +32,10 @@
  # define AC_ATC_MULTI_RATE_YAW_D           0.0f
 #endif
 #ifndef AC_ATC_MULTI_RATE_YAW_IMAX
- # define AC_ATC_MULTI_RATE_YAW_IMAX        0.222f
+ # define AC_ATC_MULTI_RATE_YAW_IMAX        0.5f
 #endif
 #ifndef AC_ATC_MULTI_RATE_YAW_FILT_HZ
- # define AC_ATC_MULTI_RATE_YAW_FILT_HZ     5.0f
+ # define AC_ATC_MULTI_RATE_YAW_FILT_HZ     2.5f
 #endif