[apps/code] Remove EditorController::m_areaBuffer

This was a very large buffer that took a lot of RAM space (the size of
the storage). Instead of having it, we just move the available space of
the storage at the end of the edited script, and move it back when the
edition finishes.
This is slower but saves a lot of space.

apps/code/script.h

@@ -26,7 +26,7 @@ public:
   Script(Ion::Storage::Record r) : Record(r) {}
   bool importationStatus() const;
   void toggleImportationStatus();
-  const char * readContent() const;
+  const char * scriptContent() const;
 };
 
 }