Have GroovePlayer init music db on creation. Make fields correctly be fk.

src/db/UserAction.h

@@ -31,17 +31,17 @@ class UserAction
 public:
     enum UAction {Login = 0, Logout = 1, RequestTrack = 2, VoteTrack = 3, UploadTrack = 4, RequestSkip = 5, Pause = 6};
     
-    User user;
+    Wt::Dbo::ptr<User> user;
     UAction action;
-    AudioTrack trackInvolved;
+    Wt::Dbo::ptr<AudioTrack> trackInvolved;
     Wt::WDateTime datetime;
     
     template<class Action>
     void persist(Action& a)
     {
-        Wt::Dbo::field(a, user, "user");
+        Wt::Dbo::belongsTo(a, user, "user");
         Wt::Dbo::field(a, action, "action");
-        Wt::Dbo::field(a, trackInvolved, "track");
+        Wt::Dbo::belongsTo(a, trackInvolved, "track");
         Wt::Dbo::field(a, datetime, "datetime");
     }