LIU-165 Docker Service Drops

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Here I've added a new type of drop known as a 'serviceapp' which essentially cannot be a leaf node in a physical graph. To demonstrate this I've added a DOCKER_SERVICE drop category that generates a DockerApp class with a serviceapp type.

Running a docker container this way will now not block execution of the graph and will automatically remove the docker container with the default removeContainer drop property.

The original Service drop can use the same serviceapp type potentially with an input application or as a group drop (will need clarification on what the desired behavior is)

EDIT: After demo some discovered nice to haves are:

• Make regular service drops work the same way when using a docker input app
• Triggering the stop node on the graph can also stop long running services
• Services may want to use different colors on the DIM session graph view (pink for running? blue for complete?)

[coveralls]

Coverage decreased (-0.2%) to 76.975% when pulling 1c500c9 on LIU-116-dockerservice-drops into 1dca409 on LIU-117-plasmaflight.

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Combining with #60