soroban milestone 1

[chatch]

Adding basic support for Soroban contracts:

• new contract view (eg. here)
  • show wasm id and available ledger details
  • download wasm button
  • raw horizon json button
• search by contract address
• render new operation invoke_host_function and types invoke_contract, upload_wasm and create_contract
  • examples: invoke_contract, create_contract and upload_wasm
• render new effects contract_credited and contract_debited (eg. here)