Avoid fatal error if someone tries to use Easy_Digital_Downloads->emails->send() before wp_mail is available.
Actually it cannot be used until init/admin_init since load_template() throws warnings otherwise
Avoid warnings due to unitialisation of attachments property, and incorrect login in get_attachments()
Various whitespace fixes
Merge pull request #2540 from leewillis77/release/2.1

Various fixes / tweaks to the EDD_Emails class