make MP4 playback speed configurable (and persistent)

[vpoluyaktov]

Before you create an issue, please make sure you have read the FAQ at https://github.com/pliablepixels/zmNinja/wiki/FAQ. Common questions on API, no image etc are covered there.

Platform & OS Version
IOS 10.2.1

The version of the app
1.2.36

Device details:
iPhone 6s

What is the nature of your issue
Enhancement

Details
MP4 player playback speed is 2x by default now. Sometimes it's not convenient and a user have to change it to see an event details. Please make the playback speed configurable.

Thanks!

[pliablepixels]

Okay, so I've changed it so that if you change the rate, it will remember the new rate and keep that persistent