dbhub: Highlight current commit in commit list

Highlight the last locally known commit id in the commit list in the
Remote dock. This should make it more obvious whether there are any
newer commits on the server.

src/RemoteDatabase.h

@@ -118,6 +118,7 @@ public:
             identity(_identity)
         {}
 
+        void clear() { name = url = commit_id = file = branch = identity = {}; }
         QString user_name() const;
 
         std::string name;