Make the word/char count a global preference

Summary:
This is an attempt to make the word/char count in the status bar
a global preference covering the whole editor instead of a temporary
menu option activated on demand for individual documents.

FEATURE: 386897

Test Plan:

1. Open Kate.
2. Open two new documents.
3. Go to Settings -> Configure Kate -> Appearance.
4. Check the "Show Word Count" option and apply changes.
5. Word counter in the status bar is shown across all documents.
6. Open another new document and observe the word counter.
7. Close Kate and open it once again.
8. The word counter is still there.

Reviewers: KTextEditor, Kate, mwolff, cullmann

Reviewed By: KTextEditor, Kate, mwolff, cullmann

Subscribers: mwolff, dhaumann, cullmann, ngraham, Frameworks

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D11822