Add editor saving/loading error messages

Previously, the editor would always say it saved or loaded a level,
even if it was not successful. For example, because a file to load does
not exist, a file to save has illegal characters in its name or the
name is too long to be stored. Now failure is reported. Also, when
quitting the editor and saving before quitting is unsuccessful, the
editor will abort quitting.

desktop_version/src/editor.h

@@ -123,8 +123,8 @@ class editorclass{
 
   int backmatch(int x, int y);
 
-  void load(std::string& _path);
-  void save(std::string& _path);
+  bool load(std::string& _path);
+  bool save(std::string& _path);
   void generatecustomminimap();
   int edgetile(int x, int y);
   int warpzoneedgetile(int x, int y);