partial fix for #2639: sign in/out has no effect if Preferences dialog is Canceled.
fix for #2616
fix for #2639: updated the 'folders to sync' dialog per spec discussion
fix for #2639: startting syncing on Preferences applied, if user is signed in
fix for #2616: make Attch.Blob use http streaming
Merge branch 'upload_file' into build
Merge branch 'build' of https://github.com/mconstantin/nuxeo-drive into Mac build