Clean up resetting editor contents and scripts

Contents and scripts should be reset in editorclass::reset(); there's no
reason to reset them again right before you load them from an XML file
in editorclass::load().

Additionally, the resets now consistently use SDL_zeroa() (for contents)
and scriptclass::clearcustom() (for scripts).

desktop_version/src/Script.cpp

@@ -35,7 +35,8 @@ scriptclass::scriptclass()
 	texty = 0;
 }
 
-void scriptclass::clearcustom(){
+void scriptclass::clearcustom()
+{
 	customscripts.clear();
 }