Allow double child without parents edge?

[chfin]

This would make analyses much more flexible. The required change to the parser is basically to not introduce mandatory edges for double ornaments, which generally should lead to more possible parses.

An example is Schumann's Träumerei: The E4 in m. 4 is a neighbor to the F4s in mm. 1 and 5, so by extension it should also be a neighbor to the F4 in the V(64) chord before, which is subordinate and thus require a connection F4@2-E4@4. We also want the F3 of the V(64) to go to E4, completing the line (A3-G3-F3)-E4, but since the F3 comes from the F3@2 of the IV chord, it would require an edge F3@2-E4@4, which conflicts with the edge F4@2-E4@4. Allowing double ornaments without parent edge allows us to express E4 as a neighbor of the F4s, but at the same time the F3 of the V(64) as leading to the E4.