The file_name fields will be used to solely indicate file paths on the
designated file system, and they are used to do normal file operations,
including file creation, file updating and file removal if needed;
added new xxx_url fields, for the URLs that should appear on DASH
manifest or HLS playlists.
xxx_url are the URIs of the media in the manifest. The fields are
converted from file_name fields but adjusted to be relative to DASH
manifest path or HLS playlist path, optionally with base_url prepended.
Previously the file_name fields are converted in place to indicate
URLs when passing to manifest / playlist builders. The original file
names were lost, which made it difficult to remove files outside of
live window.
Now that the input file names are preserved. File system APIs can
operate on the original file names while manifest / playlist generation
functions can operate on URLs.
Issue: #233
Change-Id: I36a64f16e3d1261ce91783a86588f24ad1371662
adc9549e2d