[Utils] Handle empty permissions, more checks (#387)

cogs/utils/checks.py

@@ -28,6 +28,8 @@ def is_owner():
 def check_permissions(ctx, perms):
     if is_owner_check(ctx):
         return True
+    elif not perms:
+        return False
 
     ch = ctx.message.channel
     author = ctx.message.author
@@ -75,3 +77,12 @@ def serverowner_or_permissions(**perms):
 
         return check_permissions(ctx,perms)
     return commands.check(predicate)
+
+def serverowner():
+    return serverowner_or_permissions()
+
+def admin():
+    return admin_or_permissions()
+
+def mod():
+    return mod_or_permissions()