Segmentation bugs

Create separate issues as needed:

• ctrl + move doesn't follow the mouse, when moving more than one point they get clamped up.
• merging lines more than once create new lines.
• the sign direction should be more visible especially on high resolution images.
• Sometimes when joining lines, one line seems to become shorter (result of two differing line directions???). You seem to be aware of the problem. In fact, the lines are joined and one of the lines is UNDER the other, seemingly going back. This is hard to spot because dots are on the same coordinates. One needs to move one of the points to see that there is actually sthg below.
• use text direction instead of line direction (need to detect it)
• Sometimes baselines are indicated twice, thrice or more for the same line for lines that were corrected. This is only shown when leaving the page and going back
• Lines are getting duplicated (when cutting/merging?)