Add option to disable email reply commands

Please add an option to disable the "reply commands" footer section in notification emails.  We want our users to follow our organisational process and procedure.

You may reply to this alert with these commands:
- ACK (comment) - acknowledge alert
- NEXT - escalate to next contact
- SDT X - schedule downtime for this alert on this host for X hours.
- SDT datasource X - SDT for all instances of the datasource on this host for X hours
- SDT host X - SDT for entire host for X hours