Feature: Changed Origin Offset

Currently in the code in the mouseMove function there are some harcoded values that affect which point is considered the "center" of the video. While these are simple enough to change in the source file, this should probably be a setup option.

``` javascript
this._lon = ( x / $(this.element).find('canvas').width() ) * 430 - 225;
this._lat = ( y / $(this.element).find('canvas').height() ) * -180 + 90;
```

to

``` javascript
this._lon = ( x / $(this.element).find('canvas').width() ) * 430 - this.options.viewOffsetX;
this._lat = ( y / $(this.element).find('canvas').height() ) * -180 + this.options.viewOffsetY;
```

``` javascript
$('.valiant').Valiant360({
viewOffsetX: 225, // offset for camera angle Lon
viewOffsetY: 90, // offset for camera angle Lat
});
```

Start in the mouseMove function where _lon and _lat use the hardcoded 225 and 90 offsets, then read the Valiant360 setup options shown in the issue. Add viewOffsetX and viewOffsetY as setup options and verify that configuring them changes the camera-angle offsets instead of using the hardcoded values.

Written by the indexing model from the issue text.