[NTG-context] Reorganization of the main page

Hi, After the discussions at Bohinj, I have created a new first page of the wiki. I am tried to keep things short and to the point, rather than complete. As a result a lot of links that were present in the original main page are missing. This is the first step in the effort to clean up and reorganize the wiki so that it is easier to browse. Comments are welcome http://wiki.contextgarden.net/Main_Page_New If everyone agrees with the new design, I will replace the current main page. Aditya