Removed Res::FailedCallOrCreate and added missing fields to TransactionTrace

[r3v2d0g]

Hey 👋!

Parity encodes traces results in one of two fields:

• "result" which can either store a CallResult, CreateResult or be equal to null (Res::None)
• "error" which stores a TraceError (https://github.com/paritytech/parity-ethereum/blob/master/ethcore/trace/src/types/error.rs#L25) and which Parity considers as either a FailedCall or FailedCreate

Currently, Res would only be able to decode a CallResult, CreateResult or None because it would only look into the "result" field. Thus, FailedCallOrCreate is unnecessary but Trace and TransactionTrace need an error field (TransactionTrace didn't have one).

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I also added an action_type field to TransactionTrace.

[r3v2d0g]

Maybe making our Res have the same variants as Parity's (https://github.com/paritytech/parity-ethereum/blob/master/rpc/src/v1/types/trace.rs#L434) could be done but it would probably need us to implement Deserialize for both Trace and TraceFiltering (except if there's a way to get the current JSON field's key when deserializing Res) and this would add code complexity.

We also could update the error fields from a String to a TraceError (https://github.com/paritytech/parity-ethereum/blob/master/ethcore/trace/src/types/error.rs#L25).