Migrate to Dropbox API v2

Root parameter is removed, as it must be now configured on dropbox website itself.

Thanks to Sven Franck <sven.franck@nexedi.com> for his original work on this topic.

Fix getAttachment when blob is undefined

/reviewed-on !74

Add facebook storage.
Keyless queries are case insensitive (like a fulltext search could be).

/reviewed-on !68

/reviewed-on nexedi/jio!66

This reverts commits
215a2cca
e391b71d
ddf61098
5d6e60dd
bafcf854

Add saferepair storage
Add scenario and scenario officejs in test