Fix automatic bullets

Summary:
Only create bullets automatically if 'Rich-Text' ist checked
(Settings / Editor). Non-Rich-Text notes loose their bullets
as soon as the note looses its focus or is saved.

Test Plan:
Make sure in KNotes editor settings the 'Rich-Text' checkbox is
unchecked. Create a new note, type a '-' or a '*' and some
text behind. Without the fix, an indented bullet would be drawn
in front of the text, the return key would create new lines
starting with a bullet. When clicking any other window the
bullets would disappear.
With the fix applied, no bullets are created.

Switch on the 'Rich-Text' checkbox and create a new note. Bullets
are created automatically if typing '-' or a '*' and do not
disappear when the notes looses focus. Saved notes containing
bullets still show them after restarting knotes.

Reviewers: dvratil

Reviewed By: dvratil

Subscribers: dvratil, kde-pim

Tags: KDE PIM

Differential Revision: https://phabricator.kde.org/D19443