Audience Network: add debug params to bid requests

[lovell]

Type of change

• Bugfix
• Feature
• New bidder adapter
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Does this change affect user-facing APIs or examples documented on http://prebid.org?
• Other

Description of change

Hello, this PR adds two new parameters to the bid request to help publishers when debugging.

The platform value is specific to Prebid and will not change. The adapterver value will be manually updated with any future changes to this adapter.

The now-deprecated pbv parameter, previously used for this purpose, is replaced with platver.

This work was commissioned and paid for by Facebook.

[snapwich]

@lovell it looks good to me, although it looks like you have some conflicts that need to be resolved.

[lovell]

Thanks, have rebased.

[harpere]

@snapwich had already verbally approved.