File Manager Improvments

[flauc]

We need to revisit the file manager, in its current form it isn't much better than the file manager on firebase console.

• [ ] Load more doesn't work, this is because of the cache only storing the path as reference (maybe we don't need to fix this since it will be refactored with the below changes)
• [x] Folders should be stored in firestore
• [x] It should be possible to change the icon of a folder
• [x] It should be possible to change the color of a folder
• [ ] We should keep track of how many files there are in a folder and use that for pagination via pages instead of load more. The count should be incremented/decremented in trigger functions.
• [ ] Generating thumbnails for images uploaded directly to file manager and configuring rules for how those thumbs are generate
• [x] Upload multiple files
• [x] Persist folder location in url