[APPS-1242][PRI] Add an expert sample app

:koala: :+1: 

This PR intends to add an expert sample app that shows how to use modal, promise, ajax request, underscore library, jQuery library, handlebars helper, and Lotus bootstrap(v2.3) element.

### Screenshots

#view open tickets that are assigned to the current user:
![expert_ticket](https://f.cloud.github.com/assets/5967762/1884818/11fd20e0-79af-11e3-98d8-c1ed74ba4a33.gif)

#save hook in action:
![expert_savehook](https://f.cloud.github.com/assets/5967762/1884821/378d5294-79af-11e3-9011-ac847843adba.gif)

### Note

Please test this app using your zendesk test account. Getting the search query to work locally would drag you into hell :D

### Reference

* [JIRA](https://zendesk.atlassian.net/browse/APPS-1242)

/cc @zendesk/quokka @sandlerr @princemaple @maximeprades