Added options to control adding MIME-Version and X-Mailer headers.

git-svn-id: https://plugins.svn.wordpress.org/email-users/trunk@778805 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated language translation files.

git-svn-id: https://plugins.svn.wordpress.org/email-users/trunk@778807 b8457f37-d9ea-0310-8a92-e5e31aec5664
Prep for v4.5.3 release.

git-svn-id: https://plugins.svn.wordpress.org/email-users/trunk@778808 b8457f37-d9ea-0310-8a92-e5e31aec5664
Added options to control adding MIME-Version and X-Mailer headers, improved Email Users Information panel.

git-svn-id: https://plugins.svn.wordpress.org/email-users/trunk@778809 b8457f37-d9ea-0310-8a92-e5e31aec5664
Cleaned up debug code.

git-svn-id: https://plugins.svn.wordpress.org/email-users/trunk@778810 b8457f37-d9ea-0310-8a92-e5e31aec5664