Fixes + docker-compose

[Code0x58]

• add an example docker-compose which gets a running instance on 8080 which you can use to run the example template
• get Dockerfile working again
• get tests working on python > 3.6
• fix passing of mongo username+password to child processes

It looks like there's still plenty of tidying up to do:

• Docker image doesn't have the tex packages needed to render PDF #15
• python2 support code (e.g. six) can be cleaned up as the code which requires 3.5+ (e.g. type annotates) #16
• python package requirements are not frozen, so builds will soon be non-reproducible #17
• build of docker image is not a part of the CI pipeline #18
• there are unnecessary things in tests such as assert sorted(d1.items()) == sorted(d2.items()), as well as loops over things to see where elements differ (one was removed in this PR) - the latter are not needed in pytest (unlike unittest) as it gives nice diffs when things are not equal

On the front-end's "Execute a Notebook" menu:

• hidden directories (e.g. .git) are shown #19
• "Add a new notebook+" has a bad link
• clicking on sub-menu items can collapse the menu

[jonbannister]

Thanks for the contribution! Please raise some of your points as issues and we'll get around to fixing them ASAP.