+ Extend body parsing capabilities to match with imap_fetchstructure (#…

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* + Extend body parsing capabilities to match with imap_fetchstructure
* + Improve related parsing and remove old debugging statement
* + Handle obscure "*" subtype
* + Improve processSubPartAsMessage and extractSubPartFromMessage
* + Add support for signed and pkcs7-mime messsages
* + Change the way application/json is handled
* + remove old code
* + simplified bodystructure parsing
* + fix incorrect renaming fromBodyStructure -> extractBodyStructure