Allow deploying a demo app

[djanderson]

Deploying a demo app to something like herokuapp would let people get a better understanding of the interface quickly.

Some changes would have to be made, for example, there would have to be some env var set or something that says to run the sensor in demo mode, and a "mock_acquisition" action or two would need to be provided, as well as a default user account/password, etc.

[djanderson]

1d10136 adds ability to spin up a demo sensor using docker-compose -f docker-compose.demo.yml up. Currently this just uses a sqlite database and erases the file when the container is brought down. In order to close this issue, we still need the ability to autogenerate a guest user account and enable mock/demo acquisition actions and disable any actions that require the radio.