Pr/add switchbot device list publisher

[sktometometo]

This PR add an device list interface to switchbot_ros.

~/ros/ws_jsk_fetch/src/jsk-ros-pkg/jsk_3rdparty/switchbot_ros $ rostopic echo /switchbot_ros/devices
devices:       
  -
    name: "/eng2/2f/elevator/up/button"
    type: "Bot"     
  -
    name: "/eng2/3f/elevator/up/button"
    type: "Bot"
  -
    name: "/eng2/3f/elevatorhall"
    type: "Hub Mini"
  -
    name: "/eng2/3f/new/autodoor/switch"
    type: "Bot"     
  -
    name: "/eng2/3f/old/autodoor/switch"
    type: "Bot"   
  -
    name: "/eng2/7f/73b2/bot6/button"
    type: "Bot"
  -                                    
    name: "/eng2/7f/73b2/light/lower/switch"
    type: "Bot"
  -                                    
    name: "/eng2/7f/73b2/light/upper/switch"
    type: "Bot"
  -                              
    name: "/eng2/7f/73b2/test/button"
    type: "Bot"
  -                                     
    name: "/eng2/7f/elevator/down/button"
    type: "Bot"
  -                                     
    name: "/eng2/7f/elevatorhall"
    type: "Hub Mini"
  -                                  
    name: "JSK_202012_Bot_5"
    type: "Bot"
  -                                         
    name: "JSK_202012_HubMini_2"
    type: "Hub Mini"
  -                                         
    name: "JSK_202012_HubMini_4"
    type: "Hub Mini"
  -                                  
    name: "Remote"
    type: "Remote"
---                       

[mqcmd196]

LGTM