Make browser creation actually work by postponing it until the host
window is realized and so has a valid X11 Window.
Remove unnecessary code manually creating GTK widget and just use the
standard wxGTK wxWindow instead.
Add code for setting the visual compatible with CEF to avoid X11 errors,
see https://github.com/chromiumembedded/cef/issues/3564, with many
thanks to Jiří Janoušek for finding and solving this problem originally.
Adjust the sample to handle wxWebView::Create() failure (not very
gracefully, but still better than just crashing) and to avoid using it
until it is fully created.
Update documentation to mention GTK limitations.
f5e2af9a28