Finished an example with flex
Restoring old layout for lack of flex support.
Fixed a couple of details in the menu and login overlays.
Merged frontend CSSs.
Added SASS files.

* Big refactoring of CSS styles.
Fixed some styles for responsiveness.

TODO: The header still needs to be fixed.
Small step towards responsiveness
Preview of responsive version ready.

* NOTE: Some things may be broken. Media queries need to be checked.
Refactoring of /show views
Small details fixed for mobile view.
Improved responsiveness.

* Fixed some critical layout details.
Fixed cart buttons layout and slider header padding.

* Mobile view looks pretty good now for a start.
Fixed top menu links colors.