Add IrrlichtDevice::setWindowSize (implemented only on X11, will try Windows next).
A few minor changes to the GUIEditor:
- Displays the window-size
- Update (rarely) when Window now active
- Sleep after drawing to prevent update-delays on resizing
- Driver choice now only for available drivers
- Kick out the "Tools" tab as it's unused so far and just irritating users.


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4692 dfc29bdd-3216-0410-991c-e03cc46cb475
Implement setWindowSize for Win32 device.
Note about implementation: There is already IVideoDriver::getScreenSize() which is more or less the getter for this function. But I don't think it belongs in IVideoDriver and also this function is about the window and not the screen obviously. So might make sense adding getWindowSize and deprecating getScreenSize, but that needs further changes in GUI. For now I just added a comment and let the rest be as it was.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4693 dfc29bdd-3216-0410-991c-e03cc46cb475
Bugfix: IGUIElement::addChild now prevents setting an element as it's own child (fixes for example a crash in the GUI-editor).


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code@4694 dfc29bdd-3216-0410-991c-e03cc46cb475