Add support to disable search feature.

Adding an option to explicitly disable search - This is useful in scenarios where the option list is small/simple and searching over it would be overkill.

Screenshots:

<img src="https://cloud.githubusercontent.com/assets/635679/4026166/3d7c45b6-2c10-11e4-84ca-44989398b26e.png" width="581px" height="371px">
<img src="https://cloud.githubusercontent.com/assets/635679/4026167/4083356c-2c10-11e4-9f0a-d037cef57c3e.png" width="373px" height="325px">