resource caching and XML date function, also saved from destruction

resources will now cache when downloaded, saving bandwidth.
added function to return a file's last modified date as JSON (TY Ryex)

Also, c9 (might have) ate index.php although we saved it from the depths. We are beginning to have some distrust for c9 and might use it for testing only rather than writing code. Ryex insists on having more local copies of whatever we work on from now on.