Add button actions for internal and external links.

The description will also allow links, but sometimes it's important enough to put in the button. Currently you have to hack it up with an onclick. We'll probably do that internally, but for the user-facing API it should be easier. How about:

{ action: "wikiLink", pageName: "Wikipedia:Tutorial", name: "Tutorial" }

{ action: "externalLink", url: "http://www.gutenberg.org/", namemsg: "guidedtour-tour-sometour-some-key" }

These will probably be a little different from the existing actions, in that I don't think they should use the Okay button.

I propose name and namemsg for the button text (for both), for consistency.

Version: master
Severity: normal