Refactor Guide view intent filtering for Dozuki

Viewing guides from URLs in the Dozuki app was pretty broken because the
current site wasn't updated based on the domain of the URL. This correctly
sets the current site and resets it when navigating back to already running
Activities.

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Original issue: Dozuki: Guide view navigation doesn't set the current site correctly
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Navigating to `http://test.dozuki.com/Guide/dfwe/1234` opens the guide
in the dozuki app but the site isn't changed to be `test`. Instead it is
left as whatever site was last opened.