RFC 015 proposes the introduction of data URLs to materialize static
content to files on disk. This commit adds support for data URLs to the
installer. The corresponding content will be added to versions.go in a
subsequent commit.
There used to be three definitions of a Component type, and conversion
routines between the three. Since the use case is always the same, and
the Component semantics are defined by versions.go and the installer, it
seems appropriate to define the Component type there and import it in
the necessary places.
