Update zero-network according to M2 review

[vayesy]

What needs to be done

Update code to fix issues, noted during Milestone 2 code review from Parity team.

Why it needs to be done

Increase code quality, follow best practices and high standards of the industry.

Acceptance Criteria/Task List

Fix next code issues

Runtime

• use crate repository links instead of using submodule for ORML [source]

Primitives

• use BoundedVec instead of Vec for fields in AssetMetadata struct [source]

Asset registry

• don't include metadata in asset events [source]
• log message in case of error during genesis build [source]
• merge refactor_***_native_asset into one method [source]
• split unit tests into single test case scenarios [source]

Additional context

• Add M2 review comments #169