improve build file readability.
set default values for autoselect, and default when parsing alternate audio tracks.

As specified in http://tools.ietf.org/html/draft-pantos-http-live-streaming-07#section-3.3.9
DEFAULT, and AUTOSELECT are optional, and default value is false.
list all alternate tracks in case of multiple default tracks.
extract audio from ts when selected track comes from manifest without a url
add toString functions to audio tracks.
indent with space only, remove trailling whitespace.

Identation was inconsistent, sometimes using spaces, sometimes using tabs with width 3.
To avoid indentation issues use space only.