manager: if UI_DIR is set, serve UI as well

A little hack to also serve the HTML/JavaScript UI if UI_DIR is set to
point to the ui/ directory. One could possibly do this with a
command-line option instead.
manager: remove debugging print()
manager: if serving UI, serve from /ui/

Routing patterns in Flask should be unique[1]. Serve the UI in the
development webserver from /ui and add a redirect on /.

[1] http://flask.pocoo.org/docs/0.10/design/#the-routing-system
Merge pull request #91 from rjw57/add-ui-to-development-webserver

manager: if UI_DIR is set, serve UI as well