UX "showon": Dynamic options in the Joomla Backend

Integration of the new feature made during the "Bug Squad" of the J&Beyond 2013 with Peter van Westen and myself.

The new feature allow to hide and show some elements in the configuration depending other configured elements. So the FTP options are not displayed if the FTP is not activated. Same thing for the SMTP/Sendmail options.
Different views in the configuration has been updated in order to use a new (generic) layout which support the "showon" option.