Make code cleaner

[MuxZeroNet]

The MP4 multiplexer knows where each sample is, and how to write, but it stores sample information in a complicated way. Further work is needed to improve its modularity.

• [ ] Don't make a second level in sampleInfo object. Implement data selectors for items in sampleInfo when necessary. Don't go across abstraction barriers.
• [ ] Reduce the number of parameters. Take a more object oriented approach to write new code.
• [ ] Use more concise and descriptive variable names and function names. Include comments when necessary.
• [x] Organize samples in a way that it should know which samples to write when I seek the video.
• [x] Stick to W3C definition. Correctly distinguish between INIT_SEGMENT and MEDIA_SEGMENT.