PDF template engine : add handlebars helper

[rinorway]

Espo already extends handlebars with helpers :
https://github.com/espocrm/espocrm/b...helper.js#L110
but these are only available in views.

Suggested is to make those available for email templates / pdf generation as well.

It would enhance the template engine and allow for eg filtering, for example: print only orders for an account that have been paid:

<!-- {{#each items}}-->

{{#ifEqual pay_status "paid"}}
You paid on {{pay_date}}
{{else}}
You did not pay yet.
{{/ifEqual}}

etc

[rinorway]

I have been testing and actually this works within PDF templates already :

<!-- {{#ifEqual messagetype "error"}} -->
We have an ERROR on {{system}}
<!-- {{/ifEqual}} -->

[wondertrout]

Had searched for hours before coming across this thread. Works perfectly!