Allow to customize Subject and Text for Email Reports

This PR enables three new Parameters in Email Reports: 

* **Enable Custom Email Text** Activates whether custom text is Used or Not. Also enables/disables the other two parameters on the UI. 
* **Custom Email Subject** The text to be used as the subject of the Email
* **Custom Email Text** The text to be used as the introduced text of the Email. "You can'd find the atached report text is preserverd". 

For me is quiete usable now. What do you think?