XLModel
+XLModel XLModel()
+String getCurrentAddress()
+void setCurrentAddress(String)
+Optional<Cell> getCell(String)
+boolean remove(String)
+void add(String,String)
+String getStatus()
+void clearStatus()
+void clearCell()
+void clearAll()
+void load(String)
+void save(String)
+String getAddressValue(String)
+String getAddressContent(String)
+boolean containsKey(String)
+double value(String)
+void addObserver(Observer)
+void notifyObservers()