Removed cadnano_console plugin, is now a separate plug-in, available at github.com/scholer/cadnano_console - should also be moved to using Qt-based UI.
Updated .gitignore to exclude stuff from the plugin directory, as well as a lot of standard stuff, based on github template. This allows plugin developers to add their plugins to a folder within their cadnano repository for easy testing. The alternative would be to force plugin devs to have a separate cadnano to use for plugin development.
Minor updates, mostly to non-coding parts of documentcontroller.py -- added contextmanager to file opening (according to python best practices), added a few docstrings, and removed whitespaces (was done automatically by editor).