add incomplete nodes_pinnable support
implement 'hide all links' button
add basic chosen_nodes awareness
WIP: drag-and-drop to disconnect and discard
BUGGED: discarding leaves label-less dots in the lariat
added sortedset.js
about to convert to SortedSet
converted unlinked_set to SortedSet
rename links to links_set and SortedSet
convert discarded_set to SortedSet()
WIP: node states are getting close to working well
BUGGED: dragging the last child off leaves the parent invisible