Update index.html.erb, to show nice header (especially for A1 theme when there are no Articles)

Those are for A1 Redmine theme:

*ACTUAL:*
![before](https://cloud.githubusercontent.com/assets/7809279/3211132/205be3ea-ef04-11e3-8184-b1d99dc6e2d9.png)
*EXPECTED:*
![after](https://cloud.githubusercontent.com/assets/7809279/3211133/238d2ce0-ef04-11e3-8b0e-977b64a1de2b.png)