Implement minimal contract interaction tabs and module Code+ABI

[0xfynnix]

Contract read/write is not enabled yet; we should adopt a minimal Etherscan-style Code / Read / Write interface and include ABI with modules.
Add three tabs for contracts: Code, Read, Write, following Etherscan’s minimalist approach.
Once modules support it, include both source code and ABI so that UI can render read/write forms.