This lets us use the functionality of `register_block_type` to automatically enqueue the scripts and styles used by blocks in the editor, and eventually, styles on the frontend as well. Also adds cssnano to minify our CSS.
* Add api-fetch dependency
* Remove compiled files from the repo
* Update build process, remove grunt
* Import CSS into block, as we now extract CSS via webpack to build
* Update enqueue scripts to reflect new build locations
* Detect if build files don’t exist, and instruct users to build project
* Update readme with build instructions
* Clarify where to run npm commands in info notice
* Only enqueue our JS files if we know they exist
* Clarify version compatibility between WC and WP 5.0
Kelly Dwan