Add expanding spacers as a customization option for toolbars

Authored by felixernst on Aug 1 2019, 10:58 PM.

Description

Add expanding spacers as a customization option for toolbars

Summary:
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.

Test Plan:

Reviewers: dfaure, ngraham

Reviewed By: dfaure, ngraham

Subscribers: ngraham, VDG, dfaure, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D22609