Add a Galleon layer for EE Concurrency

Minor thing. The existing 'ee' layer adds the EE Concurrency resources, which is fine. Adding a layer specific to ee-concurrency, which the existing ee layer would optionally depend on, would allow users to exclude it. Doing so wouldn't do much in terms of disk footprint, probably well under 200K. The main reason I file this is when I provision some slim servers suddenly the amount of config going to the ee concurrency resources jumps out at you. Even if the real impact of those isn't much it gives a sense of bloat.