Make summary results openskin available in openrem and make alert triggering possible

All credits for this pull request should go to Wens Kong (thanks Wens)!

• Save max. skin dose, skin dose phantom settings, and skin dose version in OpenREM

• Add option to set alerts for max. skin dose

• Fixed error if comparing none to int (in send_high_dose_alert_emails.py)

  • Python 2 could compare, Python 3 can’t

• Add max. skin dose value to alert e-mails

• Updated documentation

Refs #827