Provide i18n features

[stefanuebe]

At this point all labels and formats are hardwritten and not customizable from the server side.

It would be good to allow the devs to define the labels (e. g. for "view all") and also any formats, that are Locale dependent (at this point it should be the date format only?), e. g.:

// for our German users :)
menu.setViewAllLabel("Alle öffnen"); 
menu.setMarkAllAsReadLabel("Als gelesen markieren"); 
menu.setDateFormat("dd.MM.yyyy");