Qt port

BUGS

* crash when using the footbar and opening a file with an autosave version
  [seems the closing actions are called twice -- not supposed to happen]
* investigate random crash when adding labels to equations
  [this seems a problem with replaceButtons in the input fields in the focusbar
   probabily some objects survive the deletion and crash when trying to do
   some action on other already dead objects]

TODO

* Avoid flicker in QTMRefreshWidget
* Several problems in graphics mode.
* Check for memory leaks and non properly destroyed Qt objects.
* Implement qt_gui_rep::set_mouse_pointer, qt_gui_rep::show_wait_indicator
* Help -> (Apple) Search. How to customize this?
* Clean menu cache on language changes.
* qt_chooser_widget_rep is only partially implemented (e.g. crop images, filters, ... does not work)
* Paint interrupts on slow machines.
* Implement image_gc

DONE

* Implement glue_widget
* Russian menus.
* Handle correctly mask and quit command in texmacs_widget
* Handle correctly destroy_window_widget
* Implement "minibuffer" interactions (in the status bar)
* Visually indicate when a icon menu button is pressed.
* Missing image support.
* Remove boxes around left and right footer.
* Horizontal distance between icons too large.
* Back button when browsing help segfaults.
* Visibility of icon bars (in View menu).
* Better image support: for performance use QPixmaps in systems which support native alpha-channel (like MacOSX).
* Implement tile_menu.
* Keyboard shortcuts missing in menus.
* Support for shrinking factor.
* X should not be launched.
* Keyboard works more or less fine.
* In the documentation, rendering of keys not correct up to the pixel.
* Links don't highlight when moving over them.
* Add conversion tm_encoding -> Unicode in 'max_translate'
  (fixes <gtr> in boot message).
* Anti-aliasing should be default for all graphics operations.
* Added postscript rendering via 'convert'.
* White area of empty document should vertically extend to bottom.
* Make scrollbar(s) movable: does not seem to be supported by Qt.
* Loss of keyboard focus after clicking on icon menu entry.
* Pixmap rendering under Linux
* Invalid situation on several occasions:
  - During selections.
  - After scrolling (middle mouse) and clicking in text.
* Interactive prompts with several entries (i.e. query replace):
  all entries should appear in one window.
* Modal windows should appear inside main window,
  horizontally centered, vertically centered at height/3 from top.
* Fullscreen mode
* Header/footer visibility
* File chooser start location should be directory of current file.
* Delayed help menu, even several seconds after boot.
* In any case use QPixmap for the xpm icons (since conversion to QImage and back is costly)
