Improved footer.

* Removed information about source code (leaved only icon),
* Moved g+ and google groups icon to the left (before github icon),
* Moved shelly logo to the right (on the same level as icons at
  the left)
* Added backgroud color (the same as in header navbar),
* Changed margin and padding

![zaznaczenie_005](https://f.cloud.github.com/assets/619324/1925604/5c9051ca-7e34-11e3-85ff-263c9e92b1dd.png)