Replace deprecated methods

Summary: Some methods are considered deprecated. This patch tries to replace them with non-deprecated ones.

Test Plan:

1. Compiles with no warnings on Qt methods deprecation except for QFontMetrics::width().
2. Run k3b and create some audio project.

Reviewers: KDE Applications, aacid

Reviewed By: KDE Applications, aacid

Differential Revision: https://phabricator.kde.org/D23681