Goffice dependency

Hi all,

I'd like to make Goffice a requirement for abiword instead of using the
largely unmaintained goffice-bits. Now that Goffice license id GPL-v2 or
v3, I think the license issue is fixed. I'd keep the goffice-bits2 stuff
in until we deprecate gtk2 support.
Note that Goffice can be built without gtk support for win32 or osx
builds.
It would also help for the GtkMathView to Lasem transition about which
I'll send another mail soon since this is another story.

Cheers,
Jean