Teach cgit how to group repositories by category

The new parameter 'repo.group' is used to set the repository group
for the following repositores. Whenever this parameter changes value,
a subheading is generated in the index page (printing the current value
of repo.group).

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
diff --git a/cgit.css b/cgit.css
index 6c7f9c3..88a0a1d 100644
--- a/cgit.css
+++ b/cgit.css
@@ -353,3 +353,8 @@
 .right {
 	text-align: right;
 }
+
+table.list td.repogroup {
+	padding-top: 1em;
+	font-weight: bold;
+}