Allow central storage of API keys (#2389)

This creates a central location to store external API tokens that can be used between cogs without requiring each cog to be loaded for it to work.

A new set option for `[p]set api` is created to assist in forming bot readable API token locations.

This also updates the Streams cog to utilize the central database.

Tokens are moved from the old data locations in core cogs on load.

redbot/core/commands/converter.py

@@ -39,3 +39,29 @@ class GuildConverter(discord.Guild):
             raise BadArgument(_('Server "{name}" not found.').format(name=argument))
 
         return ret
+
+
+class APIToken(discord.ext.commands.Converter):
+    """Converts to a `dict` object.
+
+    This will parse the input argument separating the key value pairs into a 
+    format to be used for the core bots API token storage.
+    
+    This will split the argument by eiher `;` or `,` and return a dict
+    to be stored. Since all API's are different and have different naming convention,
+    this leaves the owness on the cog creator to clearly define how to setup the correct
+    credential names for their cogs.
+    """
+
+    async def convert(self, ctx, argument) -> dict:
+        bot = ctx.bot
+        result = {}
+        match = re.split(r";|,", argument)
+        # provide two options to split incase for whatever reason one is part of the api key we're using
+        if len(match) > 1:
+            result[match[0]] = "".join(r for r in match[1:])
+        else:
+            raise BadArgument(_("The provided tokens are not in a valid format."))
+        if not result:
+            raise BadArgument(_("The provided tokens are not in a valid format."))
+        return result