Caching currently implemented

Caching

• Database columns - incoming_messages (cached_main_body_text_folded, cached_main_body_text_unfolded, cached_attachment_text_clipped)

• Attachments and HTML versions of attachments - see ApplicationController foi_fragment_cache_* methods, called from InfoRequestController - on disk cache in cache dir.

• View fragment caching - see ApplicationController foi_cache, called from a couple of views - on disk cache in cache dir. Both the attachment and view fragment caches are invalidated by the AdminController expire_for_* methods.