[Verification refinement] Implement function that obtains seal data and metadata from MIME.

Ticket implements Stage 1 of the flow described in epic:

Acceptance criteria

In utilities library:

Accepts Gmail/Outlook MIME as an argument and parses it to replied/original part
Extracts seal from the original part
Extracts seal data (URL q argument)
Extracts seal PNG metadada
Returns an error in case seal was not found

In Gmail/Outlook Addons:

Use this function to obtain seal and remove all add-on specific functionality that does that.

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Edited Feb 16, 2021 by Igor Markin