Allow selecting channels with selectChats() and sendToActiveChats()

Use array for select-parameters, instead of individual parameters.

Fix #518  - Properly saving Chat IDs

Fix wrong datatype for message type.

Up and download folders are undefined by default

Allow setting a custom Guzzle HTTP Client for requests.

Some fixes and changes

Update README.md

Update DB.php

Fix 'SQLSTATE[HY093]: Invalid parameter number' PDO error which caused of multiple parameters usage in one query.