#96 discourse entity coder non-leaf choices can't be clicked

[J Carletta]

When using an ontology with the discourse entity coder, sweeping
some words and then left-clicking on a node in the ontology will
add a discourse entity to the data (containing those words, and
pointing to that node), as long as the node is a leaf. If it isn't,
nothing happens. There's no reason why not; in particular,
the coder is meant to be able to make non-leaf choices, since
it's possible to add keystrokes to the non-leaf nodes and code that
way, and since left-click has no other action assigned to it (double-click
opens and shuts that part of the ontology, not single-click). This
behaviour should be made more regular. Whoever fixes it might
want to also add an option in the configuration not to allow non-leaf
choices, since some projects wish to enforce this at software.
(Current enforcement is by not assigning keystrokes.)

Low priority until a user needs it for large-scale annotation.