fixes #235 - Small refactoring of the media handling for operating system families: * Use URI class for any URI related operations * Added substitution for $version, $major and $minor in media path * Force use of http(s)|ftp|nfs URI schema: NFS shares have now to be entered in URI form: nfs://server/path/.../ instead of server:/path/.../

removing show action in places it doesn't make sense, and minor visual changes

fixes #202 - Remove activescaffold from the medias page