[Feature] Ability to add custom collections (main folders under UPLOAD_LOCATION)

[aechmtwash]

Currently files are stored based on a user specific main folder, under the UPLOAD_LOCATION. It would be nice to be able to create additional main folders in addition to the standard user ones. These custom folders would then be assigned to users to collaborate in but would have a common storage template and would define a boundary for duplicate scans (anything within a main folder that is duplicated could be flagged for user action).

For my specific case this would allow for my wife and I to have a common collection of photos where duplicates are highlighted and eventually removed to save space, but still allowing us to have our own isolated areas where duplicates wouldn't be removed.

Uploaders (web, mobile, and cli) would have to indicate the target main folder.