Introduce basic Euclidean Rhythm (#9)

Each channel can define a euclidean rhythm by setting a number of steps (up to 16) and a number of hits to evenly distribute within those steps. CV Mod is available, however the cv mod acts as an override instead of a sum mix like the other parameters.

Refactor `applyCvMod()` so it is only called if cv mod is active for that channel. Now the setter methods will update the final output value if cv mod is not active.

Reviewed-on: https://git.pinkduck.xyz/adam/libGravity/pulls/9
Co-authored-by: Adam Wonak <adam.wonak@gmail.com>
Co-committed-by: Adam Wonak <adam.wonak@gmail.com>

examples/Gravity/app_state.h

@@ -39,6 +39,8 @@ enum ParamsChannelPage {
     PARAM_CH_DUTY,
     PARAM_CH_OFFSET,
     PARAM_CH_SWING,
+    PARAM_CH_EUC_STEPS,
+    PARAM_CH_EUC_HITS,
     PARAM_CH_CV_SRC,
     PARAM_CH_CV_DEST,
     PARAM_CH_LAST,