Implement streaming using moz-chunk-arraybuffer

Implements #4739 with `moz-chunk-arraybuffer`. Support of the http://www.w3.org/TR/streams-api/ will be easier to add.

The PDFJS.disableStream option added to disable this functionality. Currently it autodetects presence of moz-chunk-arraybuffer feature, and if enabled turns on the streaming of the PDF (in addition to range requests). The disableAutoFetch is true when streaming in process.
This is resolved below, but apart from that there appears to no further references to it in the code. Since it doesn't appear that it's passed on to any function, is this actually needed?

**Edit:** Or is this intended for use in an upcoming refactoring? In that case, a comment might be good idea.