Plugin to prevent forwarding of recent duplicate messages

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Is your feature request related to a problem? Please describe.
Sometimes the same TG users post the same info to a different telegram channels in a short time, one after another.

Describe the solution you'd like
Simple plugin to check last (5) messages we received. Drop any new message that is already in the list. Forward message otherwise, and add it to the list. Drop one element from list if it contains more than (5) element.

Later we can expand on the simple implementation to solve problems like this: #57