Allow to copy or move selection to the other split view

Summary:
FEATURE: 276167

Default keyboard shortcuts set to SHIFT+F5 for copy, SHIFT+F6 for move

Reviewers: Dolphin, elvisangelaccio, ngraham, meven, dfaure

Reviewed By: Dolphin, elvisangelaccio, ngraham, meven, dfaure

Subscribers: yurchor, kde-doc-english, dfaure, meven, kfm-devel

Tags: Dolphin, Documentation

Differential Revision: https://phabricator.kde.org/D29006