Revert "PhoneField numbers no longer assumed to be in US format"

This reverts commit a2658907a896dfc8704823ffa1ef75f5f8d2315d.

Conflicts:
	flask_common/fields.py
Revert "phonefield tests don't assume US format anylonger"

This reverts commit 359de6a294ee43028f549947c3e47ddb03ca993d.
Revert "instance -> class methods for some PhoneField actions"

This reverts commit ff301f44a82c6ae140e4be008eac9a862be1135b.

Conflicts:
	flask_common/fields.py