Mail · Reading: a message reader, a conversation, and quoted text

MailReader opens a message under its subject: the sender's picture,
name and address, who it went to, when it came, and Reply, Reply all
when it went to more than one, and Forward, each only with a handler;
then its words and its files, each downloadable. MailThreadView lays a
conversation oldest first: the newest stands open, the others fold to
a line of the sender, their first words and when, which a press, Enter
or Space opens. QuotedText folds words quoted from before behind a
small mark; open, they sit behind a rule. Long names give way at the
label width.

src/primitives/icon.rs

@@ -248,6 +248,7 @@ icons! {
     Repeat => "repeat",
     Repeat1 => "repeat-1",
     Reply => "reply",
+    ReplyAll => "reply-all",
     Rocket => "rocket",
     RotateCcw => "rotate-ccw",
     RotateCw => "rotate-cw",