No need to keep the two separate as they are tightly coupled anyway,
and the joint file doesn't become too long.

EDF is defined in terms of jobs, whether or not those jobs stem from
tasks. Make sure our definition is general enough to capture the
possibility of a set of jobs without associated tasks scheduled by
EDF.

The Prosa notion of priority-driven scheduling depends on the
preemption model. That is ok; any theory that doesn't want to deal
with non-preemptive sections can simply Require Export the fully
preemptive model and be done with it.

This fixes all warnings about ambiguous module names and resolves #49.

It also highlights that we still need to cut down on superfluous
Require Import commands in recently ported files.

Add instantiations of aRTA for
(1) fully preemptive,
(2) fully non-preemptive,
(3) limited preemptions,
(4) and floating non-preemptive regions EDF models