Fix 500 on searching on empty project, restyle search page

#### What does this MR do?

This PR fixes searching on empty projects and adds a testcase therefore. For this reason, an empty search result displays a notification message as shown below. Since this is needed for the testcase, I also do restyling of the page here.

#### Why was this MR needed?

Currently searching on an empty project raises a 500 error. 

#### What are the relevant issue numbers / Feature requests?

This PR fixes

* #7217
* #6776
* https://gitlab.com/gitlab-org/gitlab-ce/issues/119

#### TODO
* [x] Better styling if there is no search result
* [x] Extend notice message if there is no search result to issues

#### Screenshots
##### Before
![screenshot 2014-07-31 00 09 46](https://cloud.githubusercontent.com/assets/278301/3757334/ad6fa008-1837-11e4-9eae-cd1237524a79.png)

##### After
![screenshot 2014-07-31 00 05 56](https://cloud.githubusercontent.com/assets/278301/3757337/b56df48a-1837-11e4-9020-629007806e9f.png)
![screenshot 2014-07-31 00 06 44](https://cloud.githubusercontent.com/assets/278301/3757340/bd6f1844-1837-11e4-9053-bc85bb23802e.png)


I don't know how this works, but are those two strings gonna get concatenated? Should it be

```ruby
page.should have_content 'GitLab is a free project and repository \
                          management application'
```

instead?