Remove unused JSON conversion methods.

Only check if the access token is set.

Prepare url catalog properly.

Prepare access token in HetsOptions.

Adjust proof spec to the new behaviour.

Add json converting methods to HetsOptions Those are needed for async calls with sidekiq, because it can only pass basic data types to asynchronously called methods.

Return self on add.

Add method merge! on HetsOptions.

Add HetsOptions class This class shall contain all the options that are passed to hets in the json body or in the query string of an API request.