Add Tracks events to Engagement Boost

[acicovic]

Is your feature request related to a problem?

We currently don't log any Tracks events for Engagement Boost.

Describe the solution you'd like

See which events we want to track and implement that.

[acicovic]

Events to add, per @LauraKalnicky:

• Traffic Boost link click from Parse.ly menu
• Boost Traffic link click from Manage Traffic Boost page
• Boost Traffic link click from Post screen
• Accept button (automated link placement)
• Accept button (manual link placement - it would be good to know when users change the highlighted link placement text)
• Reject button
• Add Source Post