Improvements in textedit and hotkey manager

* Set textedit's cursor position to the end of text in some situations
* Send hotkey messages to the current channel instead of default channel
* Allow to overwrite sprites using otml and pngs

src/client/thingtype.h

@@ -202,6 +202,7 @@ private:
     int m_layers;
     int m_elevation;
     float m_opacity;
+    std::string m_customImage;
 
     std::vector<int> m_spritesIndex;
     std::vector<TexturePtr> m_textures;