Fix flickering in debug panel

This flickering made debug panel unusable, because most of the time
panel was white. This problem effects wxPython with GTK3+ backend
(at least on GNU/Linux systems).

Removed code IIUC draws box with content of moved debug variable, I
don't see any effect of it neither on GNU/Linux nor on Windows. It
should be safe to remove.

Fix non-usable toolbar on wxPython with GTK3+

On GNU/Linux if wxPython uses wxWidget with GTK3+ backend (this is
what most modern distributions do), then size of EditorToolBar was
always to store only one button.
This is because GetBestSize() is updated only after pane is shown and
updated.
The code does work correctly on python-wxgtk3.0 (gtk2 backend) on
GNU/Linux and with wxpython 2.8 on Windows.