Dropbox: Update to API V2

This updates to the latest Dropbox API due to the deprecations that will come on the end of September 2021.

This is for now a simple and working migration by using scoped permission and authorizeFromControllerV2 for the authorization flow.

Ideally, we should later on consider migrating to the Swift library and use the new recommended authorization flow.

This simple migration respect the same behaviour from the previous one.

Closes #1151

Note: Small issue of refresh when logging in with the Dropbox application, but it seems that it isn't a regression.

changed milestone to %3.3.0

added Cloud Maintenance labels

LGTM. Please merge once rebased locally.

added 3 commits

• 389c1c20 - 1 commit from branch videolan:master
• 2a632ea8 - Dropbox: Update to API V2
• 8e0d27c9 - URLHandler: Dropbox: Update url scheme detection

Compare with previous version

merged