Querki shouldn't be using the Global ExecutionContext

Summary: Querki is Very Very Old, in Scala terms. One of the ways this is reflected is that we are using the global EC almost everywhere. As a largely Actor-based application, this is a terrible mistake, and might explain why the system has been getting so easily destabilized lately. We need to fix it to use more appropriate ECs everywhere.

Basically, we need to comment out the global EC in querki.globals, and then fix all of the resulting errors using more appropriate ones.

This implies that we are going to need a new pathway, more or less everywhere, containing the Actor EC.

Even more importantly, we need a proper thread pool for blocking operations, and we need to use that in all places that can block. This probably needs to be available from the Ecology.

Of course, even this isn't the biggest problem: the fact that we are doing blocking DB calls inside of Actors without the right Dispatcher is a real disaster, and needs to be dealt with.