Auto-generate DSpace Sitemaps and enable by default

This has been reported based on discussions with the Google Scholar team.

They'd like to see us enable sitemaps by default and auto-update them. This would ensure that all DSpace sites have sitemaps enabled, and would avoid any issues with forgetting to enable/setup the required cron job (./dspace generate-sitemaps).

Possible options may be to:

• Generate sitemaps dynamically on request (may not be ideal for large sites, for performance reasons)
• Or, autoupdate them on a timed basis, and control that schedule in a DB or config file or similar. For example there are various Java "job schedulers" which could help to perform a scheduled task: http://java-source.net/open-source/job-schedulers
• Or, use the event system to update the sitemap on Item creation/deletion