Patch: gnome/gtk build

here is the patch :)

Adapted to the last uploaded package.

I am trying it out and making some modifications to it now.

a smaller one with the following differences compared to the previous debdiff

- don't make a new -gtk package for the plugins too since those are gnome independent already.
- do not move some files to gnumeric-common even if it makes sense, to make sure the debs install the same files as before. This can be cleaned up
later but is not needed for the gtk separation
- do not make gnumeric and gnumeric-gtk explicitely depend on the respective libgoffice, as they can work with either goffice variant. Let this
explicit dependency be stated separately if needed (in the desktop seed for example in xubuntu)
- suggest gnumeric | gnumeric-gtk for the common and the doc packages
- remove some diff hunks which only added a newline

I tested this and the resulting debs work fine with the new goffice, and the original packages install the same list of files as before this patch.

Daniel, Gauvain, unless you have further comments I'd like to commit this
by the weekend.

Upload it - it looks good to me.

thanks for the review, uploaded