sysinfo.php added in r3059

[mikelietz]

So I added a System Information page (http://trac.habariproject.org/
habari/changeset/3059) but it needs a little more polish. I see two
things that probably need work:

1) There's PHP on the page itself - the glob() for finding the user
classes belongs somewhere else - would it go in the same adminhandler
function that generates the other two sections' information?

2) Copying and pasting it from the generated HTML is less than great -
a much better support template would come from a plaintext file, which
could be generated by a function. Where would such a function go? Also
in adminhandler? Or Utils?

And a general question - would there be any usefulness to a similarly
generated complete phpinfo() from that same page?

-mikelietz