Fix start/stop/duration

[SimeonC]

Durations and start/stop weren’t displaying correctly as a “frame” has properties _start and _stop not start and stop.

I've left the "built" files out to reduce the PR size - also I'm not too clear on how gtt itself works so this just fixes the display

Fixes #16 #11

[kriskbx]

Thanks a lot for your contribution. I'm very sorry but unfortunately I cannot merge your PR because it breaks the timezone functionality within gtt.
The frame "class" has a get start() and get stop() method which takes the underlying _start and _stop parameter and applies all the timezone magic. Unfortunately these methods are not available at the renderer which leads to these errors. Instead of mapping the private _start and _stop properties, I reworked the frame object into a baseFrame class without node filesystem depedencies and a frame class with them, so the baseFrame can be used in the renderer.
Without your help it would have took me a lot longer to debug all of this, so thanks a lot again for your contribution, it's very appreciated. <3