Thanks for suggestions.
You can currently hide the mirror (or rulers) control boxes by holding down key h.
To reset a brush select “Revert to saved parameters” from the menu left of the brush name in the brush tool dock. If you changed and saved parameters of the supplied “jugi” brushes there are no commands currently to get the original version. However you can still get them if you copy the brush data files from the installation directory into the user data directory (jugipaint_instaltion_directory\stored_assets\brushes => c:\Users\your_user_name\AppData\Local\Jugilus\JugiPaint\assets\brushes)