Fixes #1.

WP has set the expectation that arguments can be specified as strings joined by ampersands. While I think it's an unnecessarily-confusing way of specifying arguments, some users seem to like it.

See http://wordpress.org/support/topic/unable-to-customise-plugin-behaviour-in-non-widget-implementation.

Introduced in e696a372.

Introduce magic getter to correct fatal error introduced in 246be76c when visibility was added to class properties

Also removed a silly call to `unregister_widget` in the deactivation hook. If the code isn't there, the widget isn't registered. (facepalm)