Toolbar: Remove slot before the popup window is deleted

This fix some strange scenario/bug where slots iterators where invalidated
in the middle of the signaling process. (The whole signal/slot impl needs
a review/simplification.)
Palettes are distributed with .gpl format now
We were calling dispatchMessages() on openPopupWindow(), which produces some messages that were deleting the toolstrip

We cannot use the "overlapped area" trick to draw the background of the
window. It's better to add a new "composite" kind of window.
More painting code from ji_screen to ui::Graphics

We planned to migrate everything to ui::Graphics to port the program to
other back-end (e.g. SDL or Allegro5). This is one step forward to that
direction.

Changes:
- Delete a lot of deprecated functions from src/ui/draw.h/cpp and SkinTheme
  that used BITMAP/ji_screen.
- Rename ui::ji_move_region to ui::_move_region
- Move ui::jwidget_get_texticon_info to ui::Widget::getTextIconInfo.
  Now the member function returns client coordinate instead of absolute
  ones.
- ui::drawTextBox() now receives a ui::Graphics instead of a BITMAP
- Add ui::Graphics::drawChar/measureChar() member functions.
- Replace ui::jrectexclude() with with ui::Graphics::fillAreaBetweenRects()
Paint PopupWindow as popup menus
Add Widget::is/setTransparent property to paint a widget merged with its background

This fixes problems with tooltips, toolbar popups and context bar popups.
It fixes issue #297 (undo notifications rendering problems).