new addon purchase_requisition_auto_rfq_bid_selection

bridge module between purchase_requisition_auto_rfq and
purchase_requisition_bid_selection
cleanup: remove useless copied code.
fix infinite recursion in super() call
[PEP8]
fix record reference in test
fix tests

follow api changes introduced in ed88ef0a
use new api in test
fix inverted condition in code
expand doc, move it to README.rst
Merge pull request #30 from gurneyalex/8.0-purchase_requisition_auto_rfq+bid_selection

new addon purchase_requisition_auto_rfq_bid_selection