[low prio] draw dependency tree

[Phaqui]

Add a graphical representation of the dependency tree. There is js code that does this in korp-frontend, but integegrating it here might not be so trivial. I haven't even checked the license.

Doing it js on the client is workable, but there isn't any reason why the api couldn't do it directly.
It could easily live under some like e.g. dependency/LANG/sentence?format=graph-tree.

[Trondtr]

If that were to work that would be a nice quickfix. another tree structure is also possible , looking like a christmas tree, contrary to the fountain found in Korp. But a fountain is certainly better than nothing.