New scripts and settings sync mechanism

[ACTCD]

After #331 and #451 are done, the mainly scripts and settings storage will use browser.storage.

We still need to preserve the ability to load and sync scripts via the file system. This requires us to implement a new set of synchronization mechanisms. It should be asynchronous and independent.

This will also be the basis for some features and optimizations. The mechanism will mainly consider data synchronization in the following locations:

• browser.storage
• iCloud sync storage
• Local file storage (macOS Only)