Tabs: Deprecate url method; use aria-controls instead of title to specify panels

We will also be keeping the href attribute unmodified and storing the panel id in the aria-controls attribute. The aria-controls attribute will be set for all tabs, regardless of whether they are local or remote. This will remove the need for the url method, which is also being removed. It will be possible to pre-define a value in the aria-controls value for remote tabs, removing the need to specify the location in the title attribute (which is also being removed).