Smart: User sync

[ytyukhnin]

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

This PR includes an implementation of the user synchronization feature for Smart's Prebid adapter. Smart is only supporting an IFRAME user synchronization.

Please use the following test parameters:

          {
            code: 'div-gpt-ad-1460505748561-0',
            sizes: [[300, 250]],  // a display size
            bids: [{
              bidder: "smart",
              params: {
                domain: 'http://ww251.smartadserver.com',
                siteId: 207435,
                pageId: 896536,
                formatId: 62913
              }
            }]
          }

and configuration:

          pbjs.setConfig({
            userSync: {
                iframeEnabled: true
          }});

As a result Smart's adapter should call the following user synchronization mechanism: csync.smartadserver.com/rtb/csync/CookieSyncV.html

This PR also includes a minor change in error logging.

[Spacedragoon]

Hello @idettman,
any news ?