Continue refactoring of AHRS and INS:
- add GEO_MAG ABI message
- add GPS ABI message
- remove explicit calling of update_gps functions (replaced by GPS ABI callbacks)
- each ins has it's own unique struct/function names
- send STATE_FILTER_STATUS from each implementation (with added id if you run multiple ones)
- use stateIsAttitudeValid() instead of AHRS.is_aligned
- The state interface is initialized with invalid attitude.
It becomes valid as soon as an attitude is set (via one of the stateSetNedToBodyX functions).
This should be only done by an AHRS/INS after it is aligned.
- add possibility to run multiple (currently two) AHRS implementations and switch which one should push the output to the state interface during runtime
`ahrs_init()` and `ins_init()` are now sort of "dispatcher" functions, that init/register the actually used implementation.
As an example using `float_mlkf` as the `PRIMARY_AHRS` and `int_cmpl_quat` as `SECONDARY_AHRS`, in your firmware section of the airframe file:
```
<subsystem name="ahrs" type="float_mlkf"/>
<subsystem name="ahrs" type="int_cmpl_quat">
<configure name="SECONDARY_AHRS" value="int_cmpl_quat"/>
</subsystem>
```
In `ahrs_init()` it calls the ahrs_x_register functions for both. Each of those calls their own ahrs_foo_init and then `ahrs_register_impl(enable_output_function)`, then do the ABI binding and register periodic telemetry functions.
The "enable_output_function" pointer is used to keep a reference to the implementation functions to switch on/off publishing of the output to the state interface.
Hence you can call `ahrs_switch(idx)` at runtime to switch the output of the AHRS implementations.
E.g. with idx=1 switch to the output of the secondary AHRS (with 0 being the primary)
Add the `conf/settings/estimators/ahrs_secondary.xml` settings file to switch them via settings.
Add cv_opticflow.xml module.
Used to for hover stabilization on an ARDrone2.
Also adds AP_MODE_MODULE to make it easier to add extra "external" control loops.
Felix Ruess
Gautier Hattenberger
dewagter
Christoph Niemann
Piotr Esden-Tempski
Freek van Tienen