End to bridge encryption implementation

So far this is passing my basic tests, but could use some testing from people
that are much more familiar with how this is supposed to work.

Refs #27

database/sqlstatestore.go

@@ -272,3 +272,31 @@ func (s *SQLStateStore) HasPowerLevel(roomID id.RoomID, userID id.UserID, eventT
 
 	return s.GetPowerLevel(roomID, userID) >= s.GetPowerLevelRequirement(roomID, eventType)
 }
+
+func (store *SQLStateStore) FindSharedRooms(userID id.UserID) []id.RoomID {
+	query := "SELECT room_id FROM mx_user_profile" +
+		"LEFT JOIN portal ON portal.mxid=mx_user_profile.room_id" +
+		"WHERE user_id=$1 AND portal.encrypted=true"
+
+	rooms := []id.RoomID{}
+
+	rows, err := store.db.Query(query, userID)
+	if err != nil {
+		store.log.Warnfln("Failed to query shared rooms with %s: %v", userID, err)
+
+		return rooms
+	}
+
+	for rows.Next() {
+		var roomID id.RoomID
+
+		err = rows.Scan(&roomID)
+		if err != nil {
+			store.log.Warnfln("Failed to scan room ID: %v", err)
+		} else {
+			rooms = append(rooms, roomID)
+		}
+	}
+
+	return rooms
+}