Add imagegrab cog: zip channel images with type-based filenames

Images are named using the message text as the filename (type tags for
WebTable card decks). Single image = text.ext, multiple = text_1.ext,
text_2.ext, etc. Falls back to messageID.ext when no text is present.

imagegrab/info.json

@@ -0,0 +1,11 @@
+{
+    "author": ["Scrapyard Cogworks"],
+    "install_msg": "ImageGrab cog installed. Use `[p]imagegrab` to zip all images in a channel.",
+    "name": "ImageGrab",
+    "short": "Zip all images from a channel with type-based filenames.",
+    "description": "Pulls every image attachment from a channel's history and sends them back as a zip file. If a message has text, images are named after that text (used as type tags for WebTable card decks).",
+    "tags": ["images", "zip", "download", "channel", "webtable", "cards"],
+    "requirements": ["aiohttp"],
+    "min_bot_version": "3.5.0",
+    "end_user_data_statement": "This cog does not store any end user data."
+}