Restored get_attribute for creddef and updated python wrapper#355

Gavinok wants to merge 2 commits intohyperledger:mainhyperledger/anoncreds-rs:mainfrom

Gavinok:restore_anoncreds_credential_definition_get_attributeGavinok/anoncreds-rs:restore_anoncreds_credential_definition_get_attributeCopy head branch name to clipboard