Fix Sharing Status screens

* Remove distinction between "shared with" and "shared by"
* Show all contacts a blog is shared with
* Show online status of contacts in sharing screen

briar-api/src/main/java/org/briarproject/briar/api/sharing/SharingManager.java

@@ -47,11 +47,6 @@ public interface SharingManager<S extends Shareable>
 	 */
 	Collection<SharingInvitationItem> getInvitations() throws DbException;
 
-	/**
-	 * Returns all contacts who are sharing the given group with us.
-	 */
-	Collection<Contact> getSharedBy(GroupId g) throws DbException;
-
 	/**
 	 * Returns all contacts with whom the given group is shared.
 	 */