License updates and metadata typo correction

CONTRIBUTING.md has a typo in its instructions stating to include the license file information as PKG_LICENSE_FILE. This should be PKG_LICENSE_FILES, per the commit that added support, r33861 from primary SVN repository.

Makefiles using the incorrect variable name are corrected.

Licensing information was added for the following packages: icecast, lftp, libtheora, ntpd.