This can be done with this quote system: [CustomAPI] Quote system
Because these commands contain private tokens, you should add them through the Nightbot web interface: https://beta.nightbot.tv/commands/custom.
Go to https://twitch.center/customapi/quote/generate. You will see three lines. Your first token is after token= and before &data= on the first line. Your second token is after token= and before &data= on the second and third lines. Replace FIRSTTOKEN and SECONDTOKEN with these before you add the following commands.
!list
$(urlfetch http://twitch.center/customapi/quote/list?token=FIRSTTOKEN&no_id=1)
!editlist
$(urlfetch http://twitch.center/customapi/addquote?token=SECONDTOKEN&data=$(querystring $(query) ))
!clearlist
$(urlfetch http://twitch.center/customapi/delquote?token=SECONDTOKEN&clear=1)
You may want to set the userlevels for !editlist and !clearlist to Moderator.