notmuch.el: Add face support to search mode

notmuch.el: Add face support to search mode

This patch use notmuch-tag-face showing tags in the notmuch-search-mode.

We can selectively highlight each tag by setting notmuch-tag-face-alist as below

(defface notmuch-tag-unread-face
 '((((class color)) (:foreground "goldenrod")))
  "Notmuch search mode face used to highligh tags.")

(defface notmuch-tag-inbox-face
 '((((class color)) (:foreground "red")))
  "Notmuch search mode face used to highligh tags.")

(setq notmuch-tag-face-alist '(("unread" . 'notmuch-tag-unread-face)
			       ("inbox" . 'notmuch-tag-inbox-face)))
(require 'notmuch)

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>