Usage: wallet.exportWallet([outputType])
Description: This method will export the wallet to the default outputType (depending on initializated params : mnemonic. HDPubKey,...).

This method varies depending from which type of wallet is this. - When init from a mnemonic, by default return mnemonic but support 'HDPrivateKey' - When init from a seed, by default returns and only support HDPrivateKey - When init from a private key, by default returns and only support PrivateKey.

Parameters:

parameters	type	required	Description
outputType	String	no	The required output type of the exported wallet

Returns : {Mnemonic|HDPrivateKey|HDPublicKey|PrivateKey}