Add labels to mobile toggle buttons according to state

[jamesmisson]

#1330 will add buttons in the mobile footer that open and close the left and right panels in mobile view.

Currently the label for this button is 'toggle left/right panel' in either state. It should adapt to the state of the panel (e.g. 'open left panel' if left panel is closed, 'close left panel' if left panel is open) like the 'more'/'less' labels on the metadata component. This should include translations for all locales.

[jamesmisson]

Welsh
Open left panel: Agor panel chwith
Close left panel: Cau'r panel chwith

Polish
"Open left panel": „Otwórz lewy panel"
"Close left panel": „Zamknij lewy panel"

French
Ouvrir le panneau à gauche
Fermer le panneau à gauche

Swedish
Öppna vänster panel
Stäng vänster panel