File system: explicitly support extensions

We should have a part of the file system dedicated to persistent data for extensions, such as configuration, logs, icons/logos, readme, and relevant user data.

Having a folder per extension would allow consistent binding rules, monitoring (to ensure data usage remains within user-specified limits), and clearing (e.g. when uninstalling, or as a refresh), and a fixed location (and filename structure?) for logs would make them easier to access and manage.

I recommend adding a shortcut (like the existing ones in the file browser), with `extensions` as the main folder, then `docker-image-name` for the individual extensions, which should include a `logs` folder for any logs, a readme file, an icon image file, a `logos` folder for company logos and the like (in case the user wants to include them in the upcoming logos section of the BlueOS interface), and anything else the extension wants to store.

Relevant to:
- #1611
- #1441
- #1243
- #1231
- #1180 (logos and readmes)

**EDIT:** We ended up deciding the directory structure of the binding should be `/usr/blueos/extensions//`.