Limit access to the "Parse.ly Stats" link

[acicovic]

Is your feature request related to a problem?

Our "Parse.ly Stats" link on the top wp-admin bar shows possibly for all users, even subscribers.

While this isn't a data disclosure concern as users need Parse.ly dash credentials to access the stats, there's no reason to show this to everyone.

Describe the solution you'd like

On first thought, 2 potential solutions:

1. Regulate access by checking for a hardcoded user capability.
2. Regulate access by providing settings similar to what we do for our PCH AI features.