Add categories for crypto status and use them
* src/gpgoladdin.cpp (OnStartupComplete): Create categories. * src/mail.cpp (Mail::update_categories): New. Set up categories based on trust. * src/mail.cpp (Mail::parsing_done): Update categories. * src/parsecontroller.cpp (ParseController::parse): Cache Signature keys in background thread.
As we are already requiureing latest gpgme this also adds
support for TOFU. A marginally trusted key with 10 or more
signatures is shown as green.