Add support for NEP-standardized contracts

[frol]

Story

As a user who uses NEP-standard contracts (e.g. NFT (NEP4)), I want to see the NEP-specific interpretation of the inputs, outputs, and state, so I can get a clear idea of the flow.

Acceptance Criteria

• [ ] Review the existing standards and contracts such as NEP4, staking pools, factories, multisig to have a clear picture of what Explorer may face
• [ ] Design the framework to support standards in a way that is extendable