Major changes ahead

- Use interact.js instead of jquery UI for dragging/resizing
  functionality

- Widgets can be resized with pinch/zoom on tablets

- Improved responsiveness by storing positional information for various
  screen widths on the item (ex. desktop, tablet, mobile).

- Stacking on mobile devices has been removed. You can achieve the same
  effect by setting the defaultSizeX to the number of columns for the
mobile mode. This is default.

- Added GridsterConfig constant to allow for setting your preferences
  site wide.

- Allow options set in the modes object in GridsterConfig to override
  the default options

- The markup to initialize the directive has been simplified to
```
<div gridster="items"></div>
```