Major TelegramClient rewrite, split it into TelegramBareClient*

Making a distinction between a bare client and a full-featured
client will make it easier to create instances of the bare
client itself that can be simultaneously and hence have two
separate connections which do not interfer with eachother.

While writing the bare client, full reconnection to a
different data center is once again done only on .connect().

telethon/__init__.py

@@ -1,4 +1,5 @@
 from .errors import *
+from .telegram_bare_client import TelegramBareClient
 from .telegram_client import TelegramClient
 from .interactive_telegram_client import InteractiveTelegramClient
 from . import tl