Update gpio/ledring drivers so they do not include "board.h". It is now

clear what all gpio/ledring drivers need to compile and what was
unnecessarily included before.
 
In attempting this it was clear that ledring had a dependency on the
multiwii code, this was removed by passing the led status update method
the values it needs.

It also turned out that the ROLL/PITCH defines were coming from
rc_alias_e and much unrelated code is coupled to these defines.  This
commit also includes some cleanups relating to that problem.

src/sensors_common.h

@@ -23,8 +23,4 @@ typedef struct sensor_t
     float scale;                                            // scalefactor (currently used for gyro only, todo for accel)
 } sensor_t;
 
-typedef enum {
-    X = 0,
-    Y,
-    Z
-} sensor_axis_e;
+extern int16_t heading;