Carry the module a request was resolved with, and give apps places (017, stage 3)

Groundwork for apps that start, stop and change on a running host, with
no change in what a host does:
- an app's module is on the heap, and the module its requests are
  resolved with is published (live, NULL while it does not run); a
  module it ran is kept while the host runs;
- a request, a view, a link's binding and a local outlet carry the module
  they were resolved with, and an owner takes none resolved with another
  (503 stopped); a local outlet finds its input again when its receiver
  runs another module, and holds its sends while it runs none;
- the published snapshot is the owner's, outliving an executor;
- apps take places, made when the host starts (--app-slots, 256), never
  given to another name, so threads find apps by name as others start.

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