Rename bot.db as bot._config (#2967)

* Rename `bot.db` as `bot._config`

  - Continues work towards strong version guarantees
  - Added methods for cog use for a few things which were previously
  only accessible via direct access.
  - Retained private use in a few internal use locations, though most
  methods were updated away from this.
  - Updated documentation for shared api token users

* changelog

* more detail

* docstring fixes

* Apparently, I forgot to commit something I had locally

  - + a copy/paste failue in the changelog

* *sigh*:

* *sigh*

redbot/core/commands/context.py

@@ -175,10 +175,7 @@ class Context(commands.Context):
         discord.Colour:
             The colour to be used
         """
-        if self.guild and await self.bot.db.guild(self.guild).use_bot_color():
-            return self.guild.me.color
-        else:
-            return self.bot.color
+        return await self.bot.get_embed_color(self)
 
     @property
     def embed_color(self):