This commit adds spacers to the kxmlgui framework so all applications
using it will be able to have any amount of spacers in their toolbar(s).
KEditToolbar gets the --- spacer --- entry by default. This entry is
modified to allow any amount of spacers to be put into the toolbars
(just like separators).
The xml scheme is updated to allow "<Spacer name="spacer_0" />" nodes
(just like separators).
KXmlGuiBuilder then builds the simple spacer by itself.