Add global comm

[hgangwar]

Moving PR #228 to here for a clean PR.

This PR introduces redev::AdiosGlobalComm to provide a global communication interface between the coupler and the applications using the existing ADIOS channel.
Usage:

auto GDI = app->AddData<pcms::GO>("global_comm", comm);

This creates a global communicator that can send and receive data, for example:

app->BeginSendPhase();
GDI->SendData(mean.data(), "mean", mean.size());
app->EndSendPhase();

app->BeginReceivePhase();
mean = GDI->ReceiveData("mean", mean.size());
app->EndReceivePhase();

• The test_GDI test case verifies global communication and data transfer.