Commands windows, add command documentation link

To help the UI auto-documentation, add a question mark toolitem at the end of the toolbar to direct the user to the TXM manual section describing the command.

The manual section is displayed in a dedicated 'TXM Manual' window.

To facilitate maintenance, we can develop and export a command documentation anchor link naming scheme in the manual.

Validation test

Open all commands editors and click on the (?) button -> the right manual section should be show in a new editor on top of the current editor