Allow tx builder ABI to be overridden

[scottrepreneur]

GitHub Issue

• Potentially closing Transaction Builder Form: ABI Paste/Fetch error #303 although there's a separate issue for the ABI parser for proxy contracts (more sophisticated solution needed)

Changes

Allows the user to override the ABI manually

Checks

Before making your PR, please check the following:

• Critical lint errors are resolved
• App runs locally
• App builds locally (run the build command for any impacted package and check for any errors before the PR)