Bundle sitemap_generator gem.
sitemap_generator configuration for published contributions and attachments.
Ignore generated sitemap files.
Add site URL configuration setting.
Add migration to init site URL config setting from relative URL root.
Infer relative URL root from site URL config setting.
Remove relative URL root from admin configuration views.
Ignore deprecated configuration settings.
Enforce no trailing slash on site URL config setting.
Ticket #87: Use site URL config setting in sitemap URLs.
Ticket #87: Associate images with contributions in sitemap.