Encourage graph connectedness

[danielhers]

TUPA often attached elements, such as Ls, Rs, and Ds, too high --- right to the top scene node instead of to the correct sub-unit. This is because when a sub-graph remains unattached, it attaches it to the root. I'm not sure how to encourage the parser to attach everything, but it does deserve some thought.

[danielhers]

Terminals are also often unattached, but currently they are not attached to the root but instead remain orphan. Those are mostly nouns + definite articles.

[danielhers]

This can be resolved similarly to #11 - by adding constraints or by post-processing.