Add support for slash command localization

[Bluesy1]

The Problem

Jishaku's sync doesn't call d.py's tree.sync(), meaning it doesn't localize slash commands

The Ideal Solution

Either call the tree.sync method, or call the translation given via Discord.py 2.0's translation system.

The Current Solution

Create a custom sync command or use !jsk py and manually call tree.sync()

Summary

Add support for Discord.py's app command localization system.

[Bluesy1]

Thanks for the super quick addition!