Fix T1073: add a basic folder mapping
Fix T1073: add a basic folder mapping

Summary: T1073 is caused by the fact we don't detect canonical folders for generic "custom" IMAP accounts because we don't have a default mapping. This diff adds this mapping. It should work for generic Cyrus servers. I didn't test it with other providers (e.g dovecot) though.

Test Plan: Tested by creating a "custom" generic account with a Cyrus server and syncing emails.

Reviewers: jennie

Reviewed By: jennie

Projects: #sync-engine

Maniphest Tasks: T1073

Differential Revision: https://review.inboxapp.com/D1471

Eagles2F/sync-engine,closeio/nylas,wakermahmud/sync-engine,ErinCall/sync-engine,Eagles2F/sync-engine,gale320/sync-engine,gale320/sync-engine,ErinCall/sync-engine,wakermahmud/sync-engine,jobscore/sync-engine,closeio/nylas,gale320/sync-engine,PriviPK/privipk-sync-engine,wakermahmud/sync-engine,PriviPK/privipk-sync-engine,Eagles2F/sync-engine,nylas/sync-engine,jobscore/sync-engine,nylas/sync-engine,closeio/nylas,ErinCall/sync-engine,jobscore/sync-engine,wakermahmud/sync-engine,Eagles2F/sync-engine,ErinCall/sync-engine,PriviPK/privipk-sync-engine,PriviPK/privipk-sync-engine,jobscore/sync-engine,Eagles2F/sync-engine,ErinCall/sync-engine,nylas/sync-engine,gale320/sync-engine,nylas/sync-engine,gale320/sync-engine,wakermahmud/sync-engine,PriviPK/privipk-sync-engine,closeio/nylas