Adpod module (prebid#3511)

* initial version of adpod module

* fix hooks, clean-up and uncomment unit tests

* correct issues in unit tests

* add missing custom key fields in fake bids for unit tests

* several updates to module and unit tests

* update logic to only add hooks once

* update targeting keys to new name

* add module description

* fix typo

* add adunit check in case of multi-format

* add exports for adpod targeting keys

* move ADPOD constant to mediaTypes.js

* undo mediaTypes change

* fix unit tests

* updates based on initial feedback

* add msg when PBC rejects bid due to duplicate key

* fix issue in videoBidCheck hook

* add buffer logic when rounding bidDuration

* add logic for deferCaching

* update logic around brandCategoryExclusion

* update support to new hook api and update logic when checking iab category field

Author: jsnellbaker