Switch URL parsing configuration to parse-url channel flag

Summary:
To avoid to hardcode the list of channel with video parsing
capability, there is now a parse-url channel flag.

Test Plan: Check it works on channels where +parse-url is defined, not on others.

Reviewers: dereckson

Reviewed By: dereckson

Subscribers: xcombelle, amj, fauve

Differential Revision: https://devcentral.nasqueron.org/D981