[V3] Ping changes (#1618)

* moves ping to core commands
defaults ping behavior to reacting with a ping pong paddle with ball
adds an optional boolean flag to ping to get the avg latency from the bot
(strikes a middle ground with intended behavior from dev standpoint, and how users want it)

* casing for @Kowlin

* use correct check for permissions

* remove latency

redbot/cogs/general/general.py

@@ -49,11 +49,6 @@ class General:
             _("My sources say no"), _("Outlook not so good"), _("Very doubtful")
         ]
 
-    @commands.command(hidden=True)
-    async def ping(self, ctx):
-        """Pong."""
-        await ctx.send("Pong.")
-
     @commands.command()
     async def choose(self, ctx, *choices):
         """Chooses between multiple choices.