GitHub uses a library called Licensee to identify a project's license
type. It shows this information in the status bar and via the API if it
can unambiguously identify the license.

This commit modifies LICENSE so that it begins with the full text of
the GPL 3.0 license. The text that was previously at the beginning of
LICENSE has been moved to the relevant section of the README, which has
been renamed to "Licensing". At the bottom of the "Licensing" section,
there is a note that mentions to the reader that they can reference
LICENSE to see the full text of not only the GPL 3.0 license, but also
all licenses related to Foreman's dependencies.

Collectively, these changes allow Licensee to successfully identify the
license type of Foreman as GPL 3.0.
Signed-off-by: Andrea Kao <eirinikos@gmail.com>