Only show Dashboard Widget to users with correct capabilities.

git-svn-id: https://plugins.svn.wordpress.org/email-users/trunk@774856 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated language translation files.

git-svn-id: https://plugins.svn.wordpress.org/email-users/trunk@774857 b8457f37-d9ea-0310-8a92-e5e31aec5664