* improve bot token validation by trying to decode user id from token
Try to decode the user id from the supplied bot token as a way of validating the token. If this should fail, indicate that the token is invalid.
* Update the tokenutils tests to pass the new validation checks
* Add test case for CheckBotTokenValidity method
* lint: clean up whitespace
* Add check for null or whitespace string, lint whitespace
* fix userid conversion
* Add hint to user to check that token is not an oauth client secret
* Catch exception that can be thrown by GetString
* Refactor token conversion logic into it's own testable method
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