mu4e: allow for displaying labels

Basic support for displaying labels.

mu4e/mu4e-headers.el

@@ -581,7 +581,7 @@ e.g. \"mutt\"."
                                            (mu4e-msg-field msg :date))))
       (:flags (propertize (mu4e~headers-flags-str val)
                           'help-echo (format "%S" val)))
-      (:tags (propertize (mapconcat 'identity val ", ")))
+      ((:labels :tags) (propertize (mapconcat 'identity val ", ")))
       (:size (mu4e-display-size val))
       (t (mu4e~headers-custom-field-value msg field)))))
 

mu4e/mu4e-vars.el

@@ -267,6 +267,11 @@ Foo\")."
         :shortname "Maildir"
         :help "Maildir for this message"
         :sortable t))
+    (:labels
+     . (:name "Labels"
+        :shortname "Lbs"
+        :help "Labels for the message"
+        :sortable nil))
     (:list
      . (:name "List-Id"
         :shortname "List"

mu4e/mu4e-view.el

@@ -823,12 +823,12 @@ Note that for some messages, this can trigger high CPU load."
               (':mailing-list
                (let ((list (plist-get msg :list)))
                  (if list (mu4e-get-mailing-list-shortname list) "")))
-              ((or ':flags ':tags)
-               (let ((flags (mapconcat (lambda (flag)
-                                         (if (symbolp flag)
-                                             (symbol-name flag)
-                                           flag)) fieldval ", ")))
-                 (mu4e--view-gnus-insert-header field flags)))
+              ((or ':flags ':labels ':tags)
+               (let ((items (mapconcat (lambda (item)
+                                         (if (symbolp item)
+                                             (symbol-name item)
+                                           item)) fieldval ", ")))
+                 (mu4e--view-gnus-insert-header field items)))
               (':size (mu4e--view-gnus-insert-header
                        field (mu4e-display-size fieldval)))
               ((or ':subject ':to ':from ':cc ':bcc ':from-or-to