Link to relevant learn articles

[jzaefferer]

Since the learn site is now online, we should deep link to relevant articles where its useful. For example, the widget pages should have links to using the widget factory. Need to figure out what else there is.

[jzaefferer]

I went through some pages.

jquery/jquery-ui#1637 adds a link on the widget demo.

jquery/download.jqueryui.com@502a282 adds a link to the API page on theming, which links to the learn site.

I don't see other places to add more links.