Some minor improvements on the validation flow of e-mail templates #23
Description
Current validation flow throws errors when setting the HTML body because it doesn't automatically clone into plain text field.
Also the $EmailTemplate/HTMLbody != empty still allows for setting the e-mail content to just an enter or space. And the same goes for the plain text variant.
Other than that the FromDisplayName cannot be set in the templates.
Maybe also add basic validation on the e-mail addresses set in From/CC/BCC/Reply-to that they are e-mails? And not just do the != empty and trim($EmailTemplate/From) = '' I mean that still allows for setting some strange stuff in there.