IMAPX refactoring: IMAPX_CAPABILITY
IMAPX refactoring: IMAPX_CAPABILITY

* moved IMAPX_CAPABILITY untagged response code to own function
  camel_imapx_server_untagged_capability()
* added TODO comments sketching the plan for imapx_untagged()
  rework

GNOME/evolution-kolab,GNOME/evolution-kolab