drag should be deprecated

WebElement.pm has a [`drag` function](https://github.com/gempesaw/Selenium-Remote-Driver/blob/fab0ee881268d0dc379ca350509f456ad8a86b94/lib/Selenium/Remote/WebElement.pm#L345) for dragging elements around, but I don't see it in the [JSON Wire Protocol][json] anymore. 

In Commands.pm, the [endpoint][] is `/session/:sessionId/element/:id/drag`; that endpoint isn't in the list. It's not on the more official [w3 spec](https://dvcs.w3.org/hg/webdriver/raw-file/default/webdriver-spec.html) either.

It seems the proper way to achieve this is to use Action chains, which we don't have in Perl (yet?).

[endpoint]: https://github.com/gempesaw/Selenium-Remote-Driver/blob/fab0ee881268d0dc379ca350509f456ad8a86b94/lib/Selenium/Remote/Commands.pm#L284
[json]: https://code.google.com/p/selenium/wiki/JsonWireProtocol