Add transfer_all to Currencies

[mzxyz]

Changes:

• Add transfer_all to currencies
• Add test for transfer_all

Not fully understand the requirements for # 375, for tokens module there has already have transfer_all function.

Further steps:

• Need to generate correct weight for transfer_all_non_native_currency

[xlc]

this needs to be free - frozen

[mzxyz]

Do you mean apply this for transfer_all in token module as we only define it in orml-tokens

[xlc]

I think the best way is add transfer_all to https://github.com/open-web3-stack/open-runtime-module-library/blob/master/traits/src/currency.rs and use it in orml-currencies

Also update the tests to check the case when user have some locked token.

[mzxyz]

I think the best way is add transfer_all to https://github.com/open-web3-stack/open-runtime-module-library/blob/master/traits/src/currency.rs and use it in orml-currencies

Also update the tests to check the case when user have some locked token.

Make sense