{,l,a}gpl-*.{tex,texi}: Proper typeset versions of the licences.

These replace the old versions `{,l}gpl.tex{,i}'.  I formatted the old
LaTeX versions by hand; I downloaded the sources for some of the new
ones from https://www.gnu.org/, and modified them slightly for inclusion
in a larger document; and I constructed the others from the plain text
versions of the licences and the upstream formatted versions I could
find.

The Texinfo sources are plain upstream versions, except that the
`gpl-2.0.texi' file is slightly modified: I've used the highlighting for
the `NO WARRANTY' section heading from the `lgpl-2.0.texi' file, because
`@heading' isn't allowed within an `@enumeration' environment in later
Texinfo versions.