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/events.py

@@ -67,7 +67,7 @@ def init_events(bot, cli_flags):
             print("Loading packages...")
             for package in packages:
                 try:
-                    spec = await bot.cog_mgr.find_cog(package)
+                    spec = await bot._cog_mgr.find_cog(package)
                     await bot.load_extension(spec)
                 except Exception as e:
                     log.exception("Failed to load package {}".format(package), exc_info=e)
@@ -243,7 +243,6 @@ def init_events(bot, cli_flags):
 
     @bot.event
     async def on_message(message):
-        bot._counter["messages_read"] += 1
         await bot.process_commands(message)
         discord_now = message.created_at
         if (
@@ -260,14 +259,6 @@ def init_events(bot, cli_flags):
                 )
             bot._checked_time_accuracy = discord_now
 
-    @bot.event
-    async def on_resumed():
-        bot._counter["sessions_resumed"] += 1
-
-    @bot.event
-    async def on_command(command):
-        bot._counter["processed_commands"] += 1
-
     @bot.event
     async def on_command_add(command: commands.Command):
         disabled_commands = await bot._config.disabled_commands()