Create Time Structure

[vaage]

To make it easier to work with samples and time in general, change time to use a structure similar to:

struct Time {
  int64_t scaled_pts;
  int64_t scaled_dts;
  int64_t timescale;
}

[rkuroiwa]

I prefer using flicks, rather than come up with our own media timescale representation.
https://github.com/OculusVR/Flicks

[kqyang]

SGTM. We may need to extend flick and use a higher resolution number though as flick is not able to handle some high frequency audio, which we may need to support: facebookarchive/Flicks#19.

[vaage]

Will will also need to standardize the type used for time between media sample and text sample. One uses signed and the other uses unsigned.