ui-tree: allow per repository override for enable-blame

The blame operation can cause high cost in terms of CPU load for huge
repositories. Let's add a per repository override for enable-blame.

Signed-off-by: Christian Hesse <mail@eworm.de>
diff --git a/cmd.c b/cmd.c
index 63f0ae5..bf6d8f5 100644
--- a/cmd.c
+++ b/cmd.c
@@ -66,7 +66,7 @@
 
 static void blame_fn(void)
 {
-	if (ctx.cfg.enable_blame)
+	if (ctx.repo->enable_blame)
 		cgit_print_blame();
 	else
 		cgit_print_error_page(403, "Forbidden", "Blame is disabled");