Feat/publish rework

[moritzkirstein]

Introduces a complete overhaul to the asset publishing process.

Implements #29
Implements #32
Implements #30
Fixes #40

Proposed Changes

• Introduce NautilusDDO wrapper class
• Update NautilusService and NautilusAsset classes respectively
• Rework the publishing flow, using a multi-step approach to
  1. Create a NFT asset
  2. Create Datatokens and Pricings for all Services of the offering
  3. Create a valid DDO with previous tsx
  4. Publish the DDO on the NFT asset
• Introduce and improve unit tests for NautilusDDO and NautilusService

Additional Information

Ignore /docs/* for review, as these are automatically generated on release. Documentation needs to be updated before 0.3.0 release.
Some tests need to be re-enabled before release.