Expose framerate in pk playback info

[TheoBendixson]

Description of the Changes

Please add a detailed description of the change, wether it's an enhancement or a bugfix. If the PR is related to an open issue please link to it.

This is an enhancement to add frame rate reporting to the standard PlayKit Playback Info.

CheckLists

• [*] changes have been done against master branch, and PR does not conflict
• [*] new unit / functional tests have been added (whenever applicable)
• [*] test are passing in local environment

I don't believe tests are relevant for this additional item

• [*] Travis tests are passing (or test results are not worse than on master branch :))
• [*] Docs have been updated

I add a comment referencing the new frames per second property