Added !unload all

Unloads all cogs at once

cogs/owner.py

@@ -75,7 +75,7 @@ class Owner:
             await self.disable_commands()
             await self.bot.say("Module enabled.")
 
-    @commands.command()
+    @commands.group(invoke_without_command=True)
     @checks.is_owner()
     async def unload(self, *, module: str):
         """Unloads a module
@@ -102,6 +102,29 @@ class Owner:
         else:
             await self.bot.say("Module disabled.")
 
+    @unload.command(name="all")
+    @checks.is_owner()
+    async def unload_all(self):
+        """Unloads all modules"""
+        cogs = self._list_cogs()
+        still_loaded = []
+        for cog in cogs:
+            set_cog(cog, False)
+            try:
+                self._unload_cog(cog)
+            except OwnerUnloadWithoutReloadError:
+                pass
+            except CogUnloadError as e:
+                log.exception(e)
+                traceback.print_exc()
+                still_loaded.append(cog)
+        if still_loaded:
+            still_loaded = ", ".join(still_loaded)
+            await self.bot.say("I was unable to unload some cogs: "
+                "{}".format(still_loaded))
+        else:
+            await self.bot.say("All cogs are now unloaded.") 
+
     @checks.is_owner()
     @commands.command(name="reload")
     async def _reload(self, module):