Fix: Error when using bigint in smart contract parameters

[limemloh]

Purpose

Closes #420.

Changes

• The injected script will now send the smart contract parameters stringified using json-bigint, which is then parsed in the extension when parsing the payload. This is all internal and should not result in any breaking changes.
• The type SmartContractParameters is extended with bigint.

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

[shjortConcordium]

I think I would prefer using our internal stringify/parse instead of adding a dependency.
It breaks the display in the popup.
otherwise LGTM.

[limemloh]

I think I would prefer using our internal stringify/parse instead of adding a dependency.

The issue with the internal stringify/parse is that it does not support arbitrary JSON, ex. if my smart contract takes the JSON { '@type': "bigint", value: "5"} then it would hit our internal representation and be replaced with 5n.

[limemloh]

It breaks the display in the popup.

I have fixed that part again