Bug 20142: Allow translating offline circ message

Bug 20142: Allow translating offline circ message

Allow translating the notification saying you cannot change branch or
logout while offline.

Test plan:

1) Enable AllowOfflineCirculation
2) Go to Home -> Circulation -> Built-in offline circulation interface
3) Try to change your branch. Note the notification message
4) Apply patch, install language, translate the notification
5) Repeat 2 and 3 in that language. The message should be translated

Signed-off-by: Pasi Kallinen <pasi.kallinen@joensuu.fi>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>