More privatization, and some error helpers (#2976)

* More privatization, and some error helpers

This makes a lot more things private. Continued from #2967, fixes #2984
Adds public methods for various things.

Below is a brief summary of things available elsewhere, though this
particular set of changes may warrant a detailed section in the release notes.

 - bot.db.locale -> redbot.core.i18n.get_locale
   - Note: This one already existed.
 - bot.db.help -> redbot.core.commands.help.HelpSettings
 - bot db whitelist/blaclist? -> bot.allowed_by_whitelist_blacklist
   - This has also been made a single cannonical function for this
   purpose including check usage
 - bot color? -> bot.get_embed_color/bot.get_embed_colour
 - bot.id.api_tokens? ->

   - bot.get_shared_api_tokens
   - bot.set_shared_api_tokens
   - bot.remove_shared_api_tokens

 -bot.db.prefix -> bot.get_valid_prefixes
   - (Note: This is a wrapper around bot.get_prefix)

 Other changes include
  - removing `bot.counter` as it was never used anywhere
  - Adding properties with helpful error messages for moved and renamed
  things
  - making bot.uptime a property with an error on set
  - adding a migration to the bot config for shared_api_tokens

* Remove overly encompassing message redaction, eval is a risk, dont run in dev if you cant manage it

* address Flame's feedback

* rephrase example

* changelog extras

* You saw nothing

redbot/core/cli.py

@@ -21,7 +21,7 @@ def interactive_config(red, token_set, prefix_set):
                 print("That doesn't look like a valid token.")
                 token = ""
             if token:
-                loop.run_until_complete(red.db.token.set(token))
+                loop.run_until_complete(red._config.token.set(token))
 
     if not prefix_set:
         prefix = ""
@@ -39,7 +39,7 @@ def interactive_config(red, token_set, prefix_set):
                 if not confirm("> "):
                     prefix = ""
             if prefix:
-                loop.run_until_complete(red.db.prefix.set([prefix]))
+                loop.run_until_complete(red._config.prefix.set([prefix]))
 
     return token