[WIP] Add preview panel for item autocomplete in Sir Trevor widgets

Closes #490 

#### Item + Text Widget
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![screen shot 2014-04-15 at 7 43 16 pm](https://cloud.githubusercontent.com/assets/96776/2715586/12b6b368-c511-11e3-80a0-ec74ef3772a8.png)

#### Multi-Up Item Grid (style) Widgets
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![screen shot 2014-04-15 at 7 43 24 pm](https://cloud.githubusercontent.com/assets/96776/2715590/2ce3869e-c511-11e3-948f-b609bd0fc31d.png)