Customize platform messages variables

Optionally add custom variables and content
- In the email body, to add a custom variable, use double curly braces (also called double mustaches). For example
```
<p>Please call your system Administrator on <strong>{{helpline}}</strong></p>
```
- Then in your properties file, set value for your custom variable
```
helpline=555 12345
```
  To return unescaped HTML as part of a template property, use the triple mustache, which is "{{{" and "}}}". The Mustache templating software that adds the property values will escape HTML variables in double mustaches by default.