desktop:computer and trash icon only show in win7mode

solve:
1.add g_signal_connect of display-mode in dock gsettings
2.keep g_signal_connect of show-computer-icon in desktop gsettings
    because it will add show computer and show trash option in right
    menu in desktop

   tower:https://tower.im/projects/1c0cd0c59ef941298c6e6b2ba6833b91/todos/4b1cdb065e2549c7ac80b88cf15ed289/

3.use g_strcmp0 instead of g_str_equal

Change-Id: I041a67360fe32b633fa676541d9f99b1ed3c790d