Allow File Attachments

[linchpinstudios]

Allow users to attach files to their forms and email them to the owner.

• Set a public $files = []; on the model to define files that should be attached.
• Setup UploadedFile object foreach $files on model
• Setup attachContent on ownerMail to get file content and attach it to the email.
• Added errors to the response of the form to return submission validation errors.