Move whitespace buttons to segment meta-panel

As discussed with Per and Remy at the user group meeting, the buttons to add whitespace to a segment simply get in the way of users, where they are in the moment.

They should be placed below the navi buttons there and should get a text "Add special characters" / "Sonderzeichen hinzufügen" above them.

They are to prominent there - and not used enough to be so prominent. So they should go to the meta-panel and the additional bar for below the segment should again only be shown, if the segment has length restrictions.

For simple view the buttons should be completely omitted. The whitespace can still be added by keyboard shortcut.

The whitespace buttons should be placed in a new box below the "save","cancel","bookmarc" etc icons.