res_http_media_cache.c: Parse media URLs to find extensions.

Use the URI parsing functions to parse playback URLs in order to find
their file extensions.

For backwards compatibility, we first look at the full URL, then at
any Content-Type header, and finally at just the path portion of the
URL.

ASTERISK-27871 #close

Change-Id: I16d0682f6d794be96539261b3e48f237909139cb