[KJots] Use KConfigDialog and KConfigXT, fix config desktop file

Summary:
This patch does following:

1. Removes KJotsConfigDlg (child of KCMultiDialog) and changes the code to just use KConfigDialog
2. Changes names of widgets in .ui-file (prepend kcfg_) to let KConfigXT take care of everything.

(this also fixes invalid signal connections to disable label/spinbox when option AutoSave is not checked)

3. Changes the layout of .ui-file to QFormLayout instead of QGridLayout with bunch of spacers
4. Fixes the inconsistency where KJots kontact plugin had name Notes, but its settings plugin used CfgDlgHierarchy=Notebooks

(because of that, KJotsConfigMisc appeared as a top-level Misc page in Kontact KCM, making in unclear which app do these settings belong)

Test Plan:

1. Changes in settings are still saved to the config
2. Misc page now appears under Notes in Kontact KCM
3. Triggering the AutoSave checkbox now correctly enables/disables the AutoSaveInterval

Reviewers: dvratil, mlaurent

Reviewed By: mlaurent

Subscribers: kde-pim

Tags: KDE PIM

Differential Revision: https://phabricator.kde.org/D29676