Add default loop patterns back into the global par_loops

[Yurlungur]

PR Summary

We discussed multiple times in the parthenon calls that we would like to reduce boiler plate, and re-introduce global par loops that don't require specifying manually an execution space or loop pattern. Here I re-introduce these defaults to reduce boiler plate.

Note that the tasking @jdolence has been working on may conflict, if he's using execution spaces for threads. (Though presumably that conflict can be resolved.)

PR Checklist

• Code passes cpplint
• New features are documented.
• Adds a test for any bugs fixed. Adds tests for new features.
• Code is formatted
• Changes are summarized in CHANGELOG.md
• Change is breaking (API, behavior, ...)
  • Change is additionally added to CHANGELOG.md in the breaking section
  • PR is marked as breaking
  • Short summary API changes at the top of the PR (plus optionally with an automated update/fix script)
• CI has been triggered on Darwin for performance regression tests.
• Docs build
• (@lanl.gov employees) Update copyright on changed files

[bprather]

I like having these. I haven't forgotten about upstreaming integrated par_for+IndexRange but this should be completely orthogonal to that.