[ptx] Usability Improvement: adjust horizont

[Rafael Nussbaum]

It would be nice, to have a tool, to indicate the line of yaw = 0, the 
horizont. This could be done by giving several point on the horizont, 
and a polynom would be fitted through these points.
Wth a lot of playing around, it can be done now.
I have for instance panoramas (not 360 °), where the first two and the 
last two images contain the horizont, but the ones in between not. This 
leads to the problem, that one of the first or last images have to be 
choosen as anchor, which gives deformations in the stitch.
To cure that, the images would have to be matched by hand to roughly 
indicate the horizont.
A tool to match the derivatives of horizontal lines over different 
images, of for instance the horizont or another horizontal line, which 
is visible in different images.
Rafael Nussbaum