Add admin sendmail

1. generate mailer UserMailer and controller sendmails 
2. add 'send mail' button for admin send mail all body at index.html.erb of users view

problem:  
   I try use smtp, application work, but not if I use sendmail  --development.rb
I direct user 'sendmail' command at bash it work. so I think whether have some 
need config I did't do.