Display conversations and groups even if they're empty.

briar-android/res/values/color.xml

briar-android/res/values/strings.xml

...android/src/net/sf/briar/android/groups/GroupAdapter.java

...id/src/net/sf/briar/android/groups/GroupListActivity.java

...oid/src/net/sf/briar/android/groups/GroupListAdapter.java

...ndroid/src/net/sf/briar/android/groups/GroupListItem.java

...net/sf/briar/android/groups/ReadGroupMessageActivity.java

...rc/net/sf/briar/android/messages/ConversationAdapter.java

...t/sf/briar/android/messages/ConversationListActivity.java

...et/sf/briar/android/messages/ConversationListAdapter.java

...c/net/sf/briar/android/messages/ConversationListItem.java