Move CloudFileService::ShowContextMenu to the base class so that all
services can utilize the pattern established in CloudFileService.
ShowContextMenu creates the menu if it doesn't exist then calls an
overridable method to populate the content. It then calls an update
method before showing the menu.
Incorrect QJsonDocument::fromBinaryData was used several places in
DropboxService. Add a single ParseJsonReply method to the base class that
properly checks and parses network replies and reports errors.
Jim Broadus
John Maguire
narunlifescience
Arnaud Bienner
Krzysztof Sobiecki