Average down faces

[WeiqunZhang]

New average_down_faces functions that take coarse Geometry and average down periodically.

Summary

Add new versions of average_down faces factions that take coarse Geometry as an argument. The average-down takes periodicity into account.

Checklist

The proposed changes:

• fix a bug or incorrect behavior in AMReX
• add new capabilities to AMReX
• changes answers in the test suite to more than roundoff level
• are likely to significantly affect the results of downstream AMReX users
• are described in the proposed changes to the AMReX documentation, if appropriate

[asalmgren]

This test fixes the lack of conservation of the no-subcycling multi-level advected scalar problem -- in a 4-level scalar advection problem we now have conservation with this feature.