v1.5 release

• Windows: prevents window being placed outside screen on laptops that were connected to external monitor before, but now are not.
• Mac: if user accidentally disallowed Imager access to removable storage, point user to security & privacy settings, instead of giving cryptic "error running authopen" error message.
• More verbose progress/error reporting
• Reconnect if download stalls for more than one minute
• Remember last selected custom image path
• Add German/French/Italian/Slovak/Turkish translations
• Windows installer: enable Installer localization
• Fix multi-level subitems_url
• Add update notification support
• Allow translators to specify external .qm file for testing
• Remove dependency on qml-module-qt-labs-settings
• Enables telemetry collecting information about which images from
  repository are most popular