Don't append base uri if chunkUrl is absolute.
Allow passing of optional parameters in MediaDrm key requests.
Stop piping PSSH information through the extractor.

It's cleaner to not inject data into the extractor only
so that it can be read out as though it were parsed from
the stream. This is also an incremental step towards
fixing Github issue #119.
Allow out-of-band pssh data for DASH playbacks.

This fixes the referenced issue, except that the MPD parser
needs to actually parse out UUID and binary data for schemes
that we wish to support. Alternatively, it's easy to applications
to do this themselves by extending the parser and overriding
the parseContentProtection and buildContentProtection methods.

Github Issue: #119