[=] Wrap fix for #555

[VoidVolker]

1. Fix for horizontal and vertical wrap. Problem was in
   getTileAtPoint: it was working only for points inside viewer - thanks
   to @avandecreme for finding this.
2. Was small bug in not rendering top row and left column - after scroll
   there are empty space and need some time for rendering.

Issue #555

[iangilman]

I've kicked it around a bit and it's looking pretty solid! A big improvement.

One thing I discovered while testing with various tile sources is that ImageTileSource and LegacyTileSource don't wrap when you turn on wrapHorizontal and/or wrapVertical. Without this patch they don't wrap at all, and with this patch they wrap just once in each direction, giving you 4 copies of the image.

Would you be up for taking a look at that issue? Here's an example tile source:

var tileSource = {
    type: "image",
    url: "/test/data/A.png"
};

[iangilman]

Actually you can just get rid of this line entirely; these subclasses inherit everything from TileSource unless overridden. Don't forget to remove the doc comment as well.

[iangilman]

Awesome, looking good! Thank you for making this fix :)