Update/tune Advanced deck section, content, headings

Reorganizes a few topics and groups them into more unified headings. Removes topics yet to be explored/detailed in a manner applicable for Kit.
Grouped indeed. That's why the title and content, including treeish and commitish is now [here](https://github.com/github/training-kit/pull/188/files#diff-bce5e08f883d72fd6f1ce5e6cc296020R9). :smile: