Set password: MDM command flow

[mostlikelee]

• Send MDM command to set password (similar flow/trigger as disk encryption)
  • on return, add Escrow activity (host-specific)
• Send MDM command to unset password (when feature turned off)
• Escrow activities should show up on both host and global feeds
• Update the stats for pending/verified/etc. -- this should not be needed since we should get it for free with the MDM command

[mostlikelee]

increasing estimate to a 13 due to added complexity of secret injection to avoid critical security issue of MDM queue storing passwords in cleartext.