[KJots] Port deprecated code

Summary:

1. Ported deprecated QPersistentModelIndex::child to QAbstractItemModel::index;
2. Ported deprecated KActionCollection::pasteText to paste;
3. Ported QStatusBar::addItem/changeItem to QStatusBar::showMessage/clearMessage (for links)
4. Removed ancient akonadi_next/note.cpp, which only held mimetype (Akonadi/Notes/NoteUtils has it);

Test Plan:

1. Just select a book or even a resource -> preview is shown for the whole book
2. Both Ctrl+V and menu action works fine
3. Hovering the text cursor over links shows destination again
4. make

Reviewers: dvratil

Reviewed By: dvratil

Subscribers: pino, kde-pim

Tags: KDE PIM

Differential Revision: https://phabricator.kde.org/D29044