Add struct cgit_page to cgit_context

This struct is used when generating http headers, and as such is another
small step towards the goal of the whole cleanup series; to invoke each
page/view function with a function pointer.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
diff --git a/shared.c b/shared.c
index 76e10d0..539d533 100644
--- a/shared.c
+++ b/shared.c
@@ -35,6 +35,9 @@
 	ctx->cfg.robots = "index, nofollow";
 	ctx->cfg.root_title = "Git repository browser";
 	ctx->cfg.script_name = CGIT_SCRIPT_NAME;
+	ctx->page.mimetype = "text/html";
+	ctx->page.charset = PAGE_ENCODING;
+	ctx->page.filename = NULL;
 }
 
 int cgit_get_cmd_index(const char *cmd)