Use Privileged Helper for file operations

[abiligiri]

Enable Xcodes.app to be used as a Standard (ie non Admin) user in managed environments. Install, rename/symbolic link to Xcode.app during activate/switch, uninstall are performed using the helper. An options in the Advanced Preferences pane added to enable/disable this feature.

https://github.com/XcodesOrg/XcodesApp/issues/112 https://github.com/XcodesOrg/XcodesApp/issues/608