[Utils] Finish and Refactor Predicate Utility (#2169)

* Uses classmethods to create predicates
* Classmethods allow using a combination of different parameters to describe context
* Some predicates assign a captured `result` to the predicate object on success
* Added `ReactionPredicate` equivalent to `MessagePredicate`
* Added `utils.menus.start_adding_reactions`, a non-blocking method for adding reactions asynchronously
* Added documentation
* Uses these new utils throughout the core bot
Happened to also find some bugs in places, and places where we were waiting for events without catching `asyncio.TimeoutError`

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

redbot/cogs/dataconverter/dataconverter.py

@@ -6,6 +6,7 @@ from redbot.core.bot import Red
 from redbot.core.i18n import Translator, cog_i18n
 from redbot.cogs.dataconverter.core_specs import SpecResolver
 from redbot.core.utils.chat_formatting import box
+from redbot.core.utils.predicates import MessagePredicate
 
 _ = Translator("DataConverter", __file__)
 
@@ -48,11 +49,10 @@ class DataConverter(commands.Cog):
 
             menu_message = await ctx.send(box(menu))
 
-            def pred(m):
-                return m.channel == ctx.channel and m.author == ctx.author
-
             try:
-                message = await self.bot.wait_for("message", check=pred, timeout=60)
+                message = await self.bot.wait_for(
+                    "message", check=MessagePredicate.same_context(ctx), timeout=60
+                )
             except asyncio.TimeoutError:
                 return await ctx.send(_("Try this again when you are more ready"))
             else: