Update translations with corrections and context

briar-gtk/briar_gtk/widgets/about_dialog.py

briar-gtk/briar_gtk/widgets/private_message.py

briar-gtk/briar_gtk/window.py

briar-gtk/data/app.briar.gtk.metainfo.xml.in

briar-gtk/data/ui/about_dialog.ui.in

briar-gtk/data/ui/add_contact.ui

briar-gtk/data/ui/login.ui

briar-gtk/data/ui/main_window.ui

briar-gtk/po/briar-gtk.pot

debian/changelog

tools/generate_data.sh