Now the status bar behavior is much more reliable on X11 systems, no more
lags when moving GoldenDict window around or when resizing it. Works
better with compositing window managers as well.
Also, the new status bar also supports images, which is good for
warnings and error messages.
The status bar is fully styled and can change its appearence
based on user's CSS, if needed.
It is a separate detacheable pane, which could also be enabled/disabled,
it tracks the current tab's contains, and lists those dictionaries that
contributed their content to the current translation.
Clicking on dictionary name jumps to the appropriate article from
this dictionary, which improves the navigation flow.
The Dictionaries Pane:
* Shows both dictionaries' names and icons.
* Does not consume resources when hidden.
* Properly styled.
* Properly handles app-wide shortcuts
(Esc, Ctrl-L, Alt-D, Enter, Alt-Up/Down).
