This makes it possible for projects using Infix as a br2-external to
override lots of OS-specific strings and contact information that
previously was hard coded.
The generated /etc/os-release now takes most of its data from .config
Worth noting is the changes in VERSION and BUILD_ID fields. The former
will be INFIX_RELEASE, during release builds, and the latter is always
the output from `git descibe ...`, or rather GIT_VERSION. This variable
can be overloaded as well.
See the help text and the new doc/branding.md document for details.
Signed-off-by: Joachim Wiberg <troglobit@gmail.com>