Enable opening app anywhere in macOS Sierra.

# How to reinstate the Anywhere setting in Gatekeeper

If the thought of having to right or control-click to open apps from
unidentified developers seems arduous and tiresome, you can turn back time with
Gatekeeper and bring back the ability to open apps from anywhere.

    # Close System Preferences to prevent overriding settings we're about to change:
    osascript -e 'tell application "System Preferences" to quit'

    # Allow opening apps anywhere:
    sudo spctl --master-disable

    # Disallow opening apps anywhere:
    sudo spctl --master-enable

Verify the change opening "System Preferences" -> "Security & Privacy", under
"General" and "Allow apps downloaded from:"... you should see "Anywhere".