scan-tree: Support gitweb.category.

Use gitweb.category from git config to determine repo's section, if
option is enabled.
diff --git a/cgit.c b/cgit.c
index ec5bbce..4656ed6 100644
--- a/cgit.c
+++ b/cgit.c
@@ -340,6 +340,7 @@
 	ctx->cfg.local_time = 0;
 	ctx->cfg.enable_gitweb_desc = 1;
 	ctx->cfg.enable_gitweb_owner = 1;
+	ctx->cfg.enable_gitweb_section = 1;
 	ctx->cfg.enable_http_clone = 1;
 	ctx->cfg.enable_tree_linenumbers = 1;
 	ctx->cfg.max_repo_count = 50;