Elefant docker support

[jbroadway]

I've started a branch with files for building Docker containers for development and production environments. The development environment can be spun up via the following commands in the root of a fresh clone of the repository:

$ make dev # build the container (only needs to be called the first time)
$ make run # spin up a development environment

The production container can be built via:

$ make build

The difference between them is that the development container points to a .docker/entrypoint.sh script that tries to run ./elefant install to create the initial database schema prior to starting Apache, while the production container marks itself installed so the Elefant installer won't run.

This presumes that you'll create the initial database schema in another way or run ./elefant install manually in production environments.

Additional commands:

$ make down # shut down the running development environment

Note: This should be considered preliminary Docker support and needs testing before being considered ready for prime time.