Image is never idle when TelegramClient is active

[LinqLover]

Describe the bug

When a TCCCore is active (e.g. has a running process), the image is never idle. In particular, this means that Shout does not work any longer because it is running in a background process with a lower priority.

Recommendations

• Run the telegram process with a lower priority (forkAt: Processsor userBackgroundPriority/systemBackgroundPriority)
• In the receive loop, insert a Processor yield between the loop iterations

Also, it would be nice to have a synchronous interface for retrieving all updates (e.g. "wait until the client is ready") ...