Issue 1055: Anchor to answer when answer is shown.

[Issue 1055](https://code.google.com/p/ankidroid/issues/detail?id=1055)

Set the webview location to where the answer begins once the answer is revealed. The desktop client simply anchors to #answer, so we do the same here. Templates by default have a ```<hr id=answer>```, so it relies on that.

The existing anchor to #question is actually not targeting anything. We don't have a ```question``` element id anywhere, so it was useless. (We do have a class, though).