dmarc: new DMARC plugin

uses dmarc_httpd from Mail::DMARC for processing and reporting
connection.js: save A-R header after data_post

so DKIM and DMARC plugins get a chance to update it
spf: store SPF results in ResultStore (was notes)
dmarc: save results in 'results' (was in a note)
dmarc: cleanup rebase litter
dmarc: use new boolean config option