Enter key

[Charles McNulty]

I just added "Enter" key support to the message list such that pressing 
Enter will open the message.

I also learned a bit more about obscure behavior in 
selecting/double-clicking/dragging messages with various mod keys 
(shift/ctrl).  Did you know that Outlook, Outlook Express and 
Thunderbird all behave differently when you click-and-hold on a message 
when the control key is held?  Me neither.  For the record Roundcube now 
emulates Outlook 2003 behavior.  I won't go into the details, suffice to 
 say you'll probably never notice the difference (but by-gum it's now 
"right"!)

-Charles