gitweb: Split git_project_list_body in two functions

gitweb: Split git_project_list_body in two functions

Extract the printing of project rows (body/contents of projects list
table) on the 'project_list' page into a separate git_project_list_rows
function. This makes it easier to reuse the code to print different
subsets of the whole project list.

[jn: Updated to post restructuring projects list generation]

Signed-off-by: Sebastien Cevey <seb@cine7.net>
Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>