Transaction execution should return a more clear error

[Fraccaman]

Right now, if a transaction fails, the client reports only which keys have been changed and which VPs have rejected the transaction. This is very confusing for a user as the reason why the transaction was rejected is not clear.
We should add the ability for to return a more clear error from the WASM execution back to the client to inform the user of what when wrong.

[cwgoes]

Could we log something from WASM during transaction execution that could be picked up by the VM and then included in the returned message?

[Fraccaman]

yeah something like this but I dont think its so easy to implement.