MultipleCurves: Change segment removal algo

Now, segments are removed in one step instead of two steps.
Previously, "both ends have degree 2+" had too much weight,
leading to failing tests cases such as a circle close to another
circle (see new test case)
MultipleCurves: Change weight formula

From now on, the angles at the segment's endpoints and the segment's
length will be used to calculate the weight.

Also segments can be replaced during post-processing. Consequently,
the order of iterating through the list is almost not relevant any
more; the algorithm ensures that the output looks good regardless
of how they are ordered.
RMST: Use normal MST instead of rectilinear