GH-1314 add UI for custom minecraft jar addition

Also changes the text of the jar mod addition button.
It should be clearer what it does and hopefully will not confuse
as many people.

application/pages/VersionPage.h

@@ -58,6 +58,7 @@ private slots:
 	void on_moveUpBtn_clicked();
 	void on_moveDownBtn_clicked();
 	void on_jarmodBtn_clicked();
+	void on_jarBtn_clicked();
 	void on_revertBtn_clicked();
 	void on_editBtn_clicked();
 	void on_modBtn_clicked();