domain-model with revised chainweb realm

[larskuhtz]

Reason:

Propose changes to #154. Mostly within the realm of chainweb

Changes made:

• add scalar values for different types of hashes that match the respective referenced types
• add time format parameter
• add non-nullable modifiers for chainweb types
• fix schema for adjacent blocks of a Block
• clarify some custom scalars by focusing on logical types. Generally, avoid representational types.
• complete schema for cut.
• Clarify the distinction between chainweb and pact realm

[Randynamic]

@all-contributors please add @larskuhtz for Code

[allcontributors]

@Randynamic

I've put up a pull request to add @larskuhtz! 🎉