Workflow for importing collections via DAT

[ikreymer]

Already have support/UI for sharing via DAT, but need interface for importing. Full Proposal: Import via DAT button on user page, along with New Collection and Upload, which would show a dialog for entering a dat, and would start sync process. If successful, external collection added to the user's list of collections. The collection is then automatically synced via Dat when it is updated. However, the user can not edit this collection as it is synced remotely. Maybe the collection is listed under a 'Watched' section for collections that are not owned by the user. The user could 'unlink' from DAT and start editing it, or copy collection to make a duplicate. Until DAT has multiwriter support, probably best we can do with collaborative editing. Note that this not needed for initial implementation, can simply be read-only at first.

This would allow sharing between individual Webrecorder Desktop instances as well as Webrecorder Desktop and webrecorder.io

[ikreymer]

(Backend DAT support tracked via #3)