[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/core/commands/context.py

@@ -6,6 +6,7 @@ from discord.ext import commands
 
 from .requires import PermState
 from ..utils.chat_formatting import box
+from ..utils.predicates import MessagePredicate
 from ..utils import common_filters
 
 TICK = "\N{WHITE HEAVY CHECK MARK}"
@@ -141,10 +142,6 @@ class Context(commands.Context):
         messages = tuple(messages)
         ret = []
 
-        more_check = lambda m: (
-            m.author == self.author and m.channel == self.channel and m.content.lower() == "more"
-        )
-
         for idx, page in enumerate(messages, 1):
             if box_lang is None:
                 msg = await self.send(page)
@@ -165,7 +162,11 @@ class Context(commands.Context):
                     "".format(is_are, n_remaining, plural)
                 )
                 try:
-                    resp = await self.bot.wait_for("message", check=more_check, timeout=timeout)
+                    resp = await self.bot.wait_for(
+                        "message",
+                        check=MessagePredicate.lower_equal_to("more", self),
+                        timeout=timeout,
+                    )
                 except asyncio.TimeoutError:
                     await query.delete()
                     break
@@ -175,7 +176,7 @@ class Context(commands.Context):
                     except (discord.HTTPException, AttributeError):
                         # In case the bot can't delete other users' messages,
                         # or is not a bot account
-                        # or chanel is a DM
+                        # or channel is a DM
                         await query.delete()
         return ret