[#16] Resolve "Support 365 mailbox instead of dovecot for incoming mails"

Closes #16 (closed)

• Upgrade imap library to latest
• Integrate OAuth authentication to Exchange 365 mailbox in IMAP

Requires ENV to be set

For XOauth2:

IMAP_AUTHENTICATION_MODE=xoauth2
SERVER=outlook.office365.com

For password:

IMAP_AUTHENTICATION_MODE=password
SERVER=cernmail.cern.ch
EMAIL=user@cern.ch
PASSWORD=password

(TBC) XOauth2 ALSO requires Etcdd Auditing env to save the refresh_token:

# Auditing
ETCD_HOST=etcd
ETCD_PORT=2379
AUDITING=True
ETCD_USER=audituser
ETCD_PASSWORD=xxx
# Default 5 minutes
ETCD_AUTH_TOKEN_TTL=60