Fix errors in kirigami example files

Summary:
Remove deprecation, fix anchors in RowLayout and remove trailing space

Done:

• Sidebar.qml
• MultipleColumnsGallery.qml
• FixedSidebar.qml
• AbstractApplicationWindow.qml // fixed crash but still very buggy

Test Plan: Using KWin transparency effect when moving windows, no pixel change found. Opening example files with qmlscene from konsole, only 4 error message left (before was more than 20)

Reviewers: Kirigami, mart

Reviewed By: Kirigami, mart

Subscribers: mart, apol, plasma-devel

Tags: Kirigami

Differential Revision: https://phabricator.kde.org/D19454