[Image] Rewrite for V3 (#768)

* [Core] add imgurpython to requirements

* [Image] v3 rewrites

* remove imgurpython from requirements

* [Image] switch to Config, add in instructions for getting imgur client id

* Add default register

cogs/image/__init__.py

@@ -0,0 +1,9 @@
+from .image import Image
+import asyncio
+
+
+def setup(bot):
+    n = Image(bot)
+    loop = asyncio.get_event_loop()
+    loop.create_task(n.set_giphy_key())
+    bot.add_cog(n)