Several GUI fixes

This time have made several GUI fixes.
- Placing (sub)windows within main middle border window
- Scrolling
- Fix issue #149
- Etc

See commit comments for more detail.
I hope you can use it in your main project.

Issue 10 is also interesting. That is the same problem I have. The list is very long and every time I must search to get the right one.

Kind regards,
Erwin