Dropbox storage deprecation

[davidjgraph]

We're deprecating dropbox as a storage option, it will no longer work after 31st December 2027.

The reason for this is the developer interface does not have a UI to roll the API secret value. Every other storage provides this. Dropbox says to submit a ticket to roll it, but in the case of a secret leak, this is absurd from a security standpoint.

The storage usage in Dropbox is extremely low, relative to other storage options. You can still open and edit the file from a locally sync'ed dropbox folder.