Add node collapsing feature

closes #30
Truncate display of long comments

Currently this only applies to CODE nodes; it might also make sense for
other nodes as well.

closes #2
treedrawing.py, settings.py, user.adoc: server mode

closes #24
treedrawing.js: disallow save while editing a node label

fix the old code to do this, and also add a last-ditch safety

fixes #32
treedrawing.js: allow using the mouse to select in edit boxes

fixes #33
News for version 1.2
version 1.2
Merge branch 'master' into aaron-dev