add submodule with a comment processing queue

Processing comments is an obvious application of this module: it's a tedious job that currently requires a lot of clicking around the UI (unless I've failed to spot a better way).

The only two operations we need are Publish and Delete, which already exist. (Though they need to be tweaked a little to work with non-Entity API entities.)

So this is a fairly simple module to put together, and acts as a nice demonstration of HQW. It's also quite useful!