t8n tool improvements

[gurukamath]

The current t8n tool, although fully functional has a lot of room for improvement. An update /re-build of the tool might be in order. The following improvements would be good to have

1. Updates to the specs are automatically reflected in the t8n tool without a need for explicitly updating it
2. Improve tracing implementation
3. Make the t8n tool code more maintainable. (re-factor/re-build components)
4. Implement a tighter type system
5. Reduce code duplication with other spec tools

[gurukamath]

Some re-factoring of the code is being considered which might impact this issue (potentially make the t8n improvements easier). See this for more details.

[marioevz]

I would add to here (just to not creating a duplicate issue) to have better exception messages returned when a transaction in the list is invalid.

Right now we receive the same error for every different kind of exception:

"rejected": [
        {
            "index": "0x1",
            "error": "Failed transaction: "
        }
    ],

And in EEST we have a mapper to try to catch test errors when the error that the test triggers is not the error that needs to be hit by the test vector.