Feature: allow to configure the main module of LFEditor in the BE

It would be usefull to configure where LFEditor module is displayed in the backend.

Since TYPO3 8.7, the "user" main module is now a dropdown in the top bar, and LFEditor is inserted there. I would suggest to allow integrator to chose where LFEditor is displayed with an option in the extension configuration.

The options could be:

• user (default, like today)
• system
• tools
• web