Extracted group strings for translation + minor fix for outgoing update
- translations were not possible for group emphasises
- outgoing updates were shown as "... joined the group. Title is now ..."
  rather than "Group updated.". Translators should mind that there can be
  one or many recipients that have joined!
Merge remote-tracking branch 'origin/l10n_group_2nd_attempt' into l10n_group_2nd_attempt