[2.2] Add search web capabilities to menu applet

Gives the options of searching Google, Duck Duck Go and Wikipedia
![screenshot from 2013-08-03 19 01 59](https://f.cloud.github.com/assets/1336336/905471/48b720fa-fc2c-11e2-8239-b852a32c1ec2.png)

TODO:
A couple of things:

- Better search engine icons
- Yahoo could be added, but the locale would have to be checked (it's a different Yahoo depending on it, and it's not available for all locales)