Upgrade composer files to newer version

[NeillM]

Newer version of the composer file syntax have some nice features that might make it worth upgrading to use them.

for example 2.1 added the ability to define health checks, see an example of using healthchecks

If we did this we might be able to automatically run scripts that wait for the database to be ready and the app to be up as part of the start up process of the containers.

We might also be able to add things that would detect and recover from situations like Selenium crashing.