[Pharo-project] pharo-project.org: small updates website

[Marcus Denker]

Hi,

-> The download button now goes to http://www.pharo-project.org/pharo-download, 
not the zip (because there are now 3)
-> updated http://www.pharo-project.org/pharo-download for the platform 
specific zip files
-> added a page for GSOC: http://www.pharo-project.org/community/google-soc

        Marcus