[BUG #8017] qx.Mobile should support new Flex Syntax
*  Update of Picker
[BUG #8017] qx.Mobile should support new Flex Syntax
*  Refactoring of gap solution of Atom
[BUG #8017] qx.Mobile should support new Flex Syntax
*  Refactoring of gap solution of Atom
[BUG #8017] qx.Mobile should support new Flex Syntax
* Refactoring of flex CSS classes.
[BUG #8017] qx.Mobile should support new Flex Syntax
*  Update of Dialog widget
[BUG #8017] qx.Mobile should support new Flex Syntax
*  Update of List widget
[BUG #8017] qx.Mobile should support new Flex Syntax
*  Refactoring of gap solution of Atom
[BUG #8017] qx.Mobile should support new Flex Syntax
*  Update of Label widget
Minor improvement of Mobile Showcase
[BUG #8017] qx.Mobile should support new Flex Syntax
*  Update of Card layout
[BUG #8017] qx.Mobile should support new Flex Syntax
*  Renamed CSS classes
Minor
Added getFlexboxSyntax() method for detecting which syntax is supported by browser.