Add e-mail as a monitor service for the JobScheduler Monitoring Interface

Desired Behavior

• The JobScheduler Monitoring Interface should support e-mail as a monitor.
  • The Mail Monitor can be configured similar to any System Monitor such as Nagios, op5 etc.
  • Service configurations apply to mail, e.g. by using different mail configurations as a services for different sources (jobs, job chains)
• Mail is configurable to some extent:
  • Recipients: To, Cc, Bcc
  • Format: html, plain text
  • Subject and Body with a replacement mechanism for all attributes available with the Monitoring Interface
• Mail can be used for info messages, error messages and recovery messages