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
Merge pull request #13 from smt116/master

Improved footer.