Add social links: twitter and facebook icons to the KEXI menu.
(don't break branding requirements)
Facebook: shows https://www.facebook.com/kexi.project on click
Twitter: shows https://twitter.com/kexi_project on clicks
```
| menu |
| |
| |
| calligra |
| |
| Join us on: F T |
-------------------
```
PS: add G+ later