Replace common module with validate module. Move validation function from feed module to validate module and remove feed.py. Correct any usage of validation functions from common and feed modules into validate module.
Patch by: Pawel Solyga
Review by: to-be-reviewed
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"Todd Larsen" <tlarsen@google.com>
"Sverre Rabbelier" <sverre@rabbelier.nl>
"Pawel Solyga" <pawel.solyga@gmail.com>