Bug Contexteditor scrollbars

[DavidBormann]

If you use the arrow-keys in a large context the scrollbar do not notice it

[eugenkiss]

Yes, that's indeed a problem. I'm pretty sure I just need to not only update the position of the selection but also of the (in our case invisible) "lead anchor". Nonetheless, this bug hunt could turn into several hours of work which I can't invest now. If somebody reminds me I will fix this bug in a couple of months.

[blu2lz]

After reducing context I get ArrayOutOfBounds exceptions in the table model. Not breaking functionality but not pretty at all. I guess there's something severely wrong in the table model. I will investigate when I fix this issue and #43.