It should be possible to allocate parrays before a device manager exists.

[wlruys]

Issue in title.

In the current code base PArrays can only be created once inside a with Parla() region because they rely on the size of the device manager. For general programmability, PArrays should be able to be declared with a lifetime greater than the parallel Parla region.

I think the last time I looked into this, the Task Dataflow object would need to be refactored.