Disabled and hid Base64 option as it not currently working.

git-svn-id: https://plugins.svn.wordpress.org/email-users/trunk@994721 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated German translation (Dieter Menne)

git-svn-id: https://plugins.svn.wordpress.org/email-users/trunk@994727 b8457f37-d9ea-0310-8a92-e5e31aec5664