Credentials - full support

[Anna15170221]

We need to add full support for Credentials - for all fields and flags.
Docs:
https://github.com/XRPLF/XRPL-Standards/tree/master/XLS-0070-credentials

Tx and object examples:
Credential:
https://dev.bithomp.com/en/object/BA3520056B86932FC72015EDA1C512A9902B79028F42AF83993DA470AE2F5A5F

CredentialCreate
https://dev.bithomp.com/en/tx/8D3EA1549CCF578479645906F98075FEC3C8110D2DC7C56F20BEE49F6B55AB84

CredentialAccept
https://dev.bithomp.com/en/tx/E6A0503E311C9A68A948CC7C4CCE3DA307272A8E7E307F05313D2634BAD58BF9

CredentialDelete
https://dev.bithomp.com/en/tx/5AA77FFA41A09C6EE580A4DB98D904CFD3EA655C226B83E7DA0BD01E6B3F5CD6

/v3/transaction/:hash

DepositPreauth

Updated specification
specification.authorizeCredentials[]
specification.unauthorizeCredentials[]

fromat of each record
  issuer - address
  type - text decoded from hash, if possible

example:  https://dev.bithomp.com/api/cors/v3/transaction/7B389165302FE0CC8BE918EAAC4D5B2589F055A6FD40EC31D785FB4A09EFD22F

[ihomp]

@Anna15170221 all examples seems like outdated, transactions are not available.
Please ask @ildaruz for new examples.

and test that we show the information

[Anna15170221]

@ihomp I've tested, but probably you'd better have a look yourself too.
new examples:
https://bithomp.com/en/tx/B8A4AA4FC836E47037A9A8D01CE128B5C7EFA807D13414141CE734AC183B6223
https://bithomp.com/en/tx/BA8729E8A2783000F4457D71BADF59B4DD6E7AB4649B238A4BF1A1100B9B6200
https://bithomp.com/en/tx/23C5D4BED0DA41FBF718014D772BDD31CAA21FF2D53919DE2F426FA83FF2F2BE
https://bithomp.com/en/tx/7A14C92D244681D0F0B98AED6BC7166CD2FCFB325C615CB2F7A5D67E04D71410

[ihomp]

I need DepositPreauth transactions with Authorize/Unauthorize to test the PR @Anna15170221 @ildaruz @pandablue0809