Original API used in the example is no longer free, so while following the tutorial I found a different API to use in the tutorial and updated the example code to match the new API. Also made a few small changes.
Update Build-a-connector tutorial
* Update screenshots and instructions to match current UI
* Update code examples to use Polygon.io API
* Add links to language-specific guides
* Consistently use Python (uppercase P) when referring to the language
and python (lowercase) p in code samples
* Consistently do not use "." in lists
* Add an image of Airbyte startup banner
* Add a note for M1 macs
* Remove unused images
* Make Dockerfile consistent with the tutorial
