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.

Fix problem with decreasing size of StatusToolBar when tools are removed from toolbar.

StatusToolBar - toolbar with tool to build, clear, connect, ...
This problem appears only in python-wxgtk3.0. In python-wxgtk2.8 there
was not such problem.

If call StatusToolBar.SetMinSize(wx.DefaultSize), all is working, but
following warning message appears:

(Beremiz.py:15155): Gtk-WARNING **: 18:42:24.115: Negative content
width -6 (allocation 1, extents 4x3) while allocating gadget (node
toolbar, owner GtkToolbar)

To avoid that StatusToolBar.GetToolBitmapSize() is used instead of wx.DefaultSize

Add BACnet example

Rework README.md, add examples section, add instructions for Modbus extension, more information about runtime.