Clients::Studio: fixed drawing element

    * src/clients/studio/elementitem.cpp: corrected drawing element item
      when element's name was longer than pads size.
Clients::Studio: implemented detecting under-object during  linking

    * src/clients/studio/mainwindow.cpp: added one more element, for tests
      purpose.
    * src/clients/studio/paditem.cpp: detecting under-object on
      mouse-motion event.
    * src/clients/studio/paditem.h: declared quark, which is identifier of
      parent pad of internal objects (Text and Rect).