Add "flags3d" flag collection

We need a way to be able to select between separate sets of icons before replacing the current one. Please see #319966: Add flag icon theme selector if you want to help. (Also, there is a Romanian flag in the 6.x-1.0 release.)

Also, if you could provide any information on the usage terms on this icons, that would also speed up the process of adding them, once the above mentioned issued has been resolved.

"All documents published through LinuxFocus prior to August 2004 are available under the terms of the GNU Free Documentation License with no Invariant Sections, no Front-Cover Texts and no Back-Cover Text."
Icons date back to 2002. Later stuff is under Attribution-NonCommercial-ShareAlike License.

But if we add them here, we'll publish them under the GPL. Unfortunately, both the GFDL and CC by-nc-sa licenses are incompatible with the GPL. So we can't include this. :(