Adding support for Adafruit PCA9685 servo controller

[zuccon]

This PR adds support for building a Brachiograph using an Adafruit PCA9685 I2C controller instead of pigpio.
More background information in the README

Some refactoring has been done to avoid code duplication:

• The Plotter class has been split into a common subclass and hardware-specific classes.
• Virtual mode is now just another hw-specific class.

Documentation will be updated if the change is accepted. In that case, also how to build a PCA9685-based Brachiograph will be documented.

Thanks for the Brachiograph fun!

[evildmp]

Thanks, this is great to see, I have no way of testing this right now, but I am doing some work on the project so let me think about this a bit to see how to incorporate this approach.

[NonaSuomy]

Was this ever included?
It is a fairly priced module https://www.aliexpress.com/w/wholesale-pca9685.html?catId=0&initiative_id=AS_20230603063046&SearchText=pca9685&spm=a2g0o.home.1000002.0

[LouDou]

I would also like to see this merged; unfortunately it doesn't rebase on master. Also, before I noticed this PR I also made similar changes, to be able to swap out the hardware driver part. I wrote a simple adapter to use the same Adafruit libraries. My branch is based on master as of today:

https://github.com/LouDou/BrachioGraph/tree/feature/basic-pca6985