moduleConfigurations: TaskKey

I'd like to convert moduleConfigurations to a TaskKey.
The reason is that it doesn't *have* to be a SettingKey (it's only used in tasks), and as it is, it limits how much you can achieve with it --
Specifically, I'd like to add a moduleConfiguration that forces packages from my company to use our own bespoke chain resolver, which will only query the local ivy and our internal ivy repositories.
However, by doing that, I can't add the inter-project resolver anymore -- it's created by a task, and as I can see, it's only automatically propagated into "sbt-chain", which is what I've been trying to avoid. 

To summarize, if moduleConfigurations were a task I could easily do something like:
```
moduleConfigurations <+= (organization, internalResolver, projectResolver) map { (o,ir, pr) =>
    ModuleConfiguration(o, ChainedResolver("internals", Seq(pr, Resolver.defaultLocal, ir))
}
```

Whereas now I can't add `projectResolver` and so I can't use this set-up for a multi-project build.