add authorized publishers, update DDO validate call

[paulo-ocean]

Fixes #91

Changes proposed in this PR:

• Add AUTHORIZED_PUBLISHERS to ci ( node only adds signature to addresses on AUTHORIZED_PUBLISHERS or AUTHORIZED_PUBLISHERS_LIST)
• needs updated validate call (validate ddo) and updated sdk (as we need to add a signature)
• NOTE: tests will fail until we merge the SDK changes add validate function signature changes, missing update docs and others ocean.js#1914 since the function signature changed

[jamiehewitt15]

Looks good to me

[jamiehewitt15]

NOTE: tests will fail until we merge the SDK changes oceanprotocol/ocean.js#1914 since the function signature changed

Let's merge that one first then