Add support for string concatenation/manipulation in jetEngine forms

[enumans]

Currently it's possible that a specific field value in jetEngine forms can be calculated. For example, a price total can be automatically calculated by using values of other fields.

This is a great feature, but only works with numbers at the moment. I'd like to use this to manipulate (add) strings as well.

Some examples:

• Combine the custom fields 'first name' and 'last name' into a Post Title. Something like: _post_title = firstname+' '+lastname
• Combine an address field and a city field to use as a location for a map listing.

Thanks.

[Gabrymi93]

+1 Calculated text field is a must! Thanks