added python-xml in archeos-meta (archeos-graphics)

[Luca Bezzi]

Hi all,
I just added the library python-xml to the metapackage archeos-graphics. 
This library is necessary to export "optimized svg" from Inkscape. Tis 
file format is a simplified svg, whose code is extremely compatible with 
js graphic-oriented open source libraries, like Raphael (useful in 
showing archaeological data through internet). It is a small 
modification that optimize Inkscape fo an archaeological use, without 
contraindications.

Ciao.