display of enhanced dependencies arcs

[jonorthwash]

The enhanced dependencies currently display as black arcs.

@ftyers suggests:

In focus should be black, out of focus should be dotted. So e.g. if you're in enhanced mode, the basic deps are dotted and if you're in basic mode the enhanced ones are dotted.

See #178 (comment) .

[Zensho]

The dotted example would look something like this, is this preferable?

[jonorthwash]

@ftyers says it looks good to him!

[jonorthwash]

(I kind of like grey better, but that's currently used for dependencies without deprels, I think? Maybe the two styles could be switched at a later date if that were consensus. Anyway, this is bikesheding, so ignore.)