api: use flask-script for development server

The "idiomatic" way to have a ``ruaumoko-api``-like tool with flask is
to use Flask-Script's manager object. For one line of code, we get the
same support which we previously had along with the ability to specify
bind address and port which is occasionally useful. It also supports
live-reloading of the Python module which is almost always useful for
development.
manager: add configuration from environment

For the development web server the environment variable
``RUAUMOKO_SETTINGS`` may now optionally be set. If it is set, it points
to a configuration file which can be used to configure the webapp
settings including, but not limited to, the path to the ruaumoko
dataset.
manager: add copyright banner

Add copyright banner which should be atop all source files.
Merge pull request #25 from rjw57/use-flask-script

make the development webserver useful for development