Add validate transaction method

[shuse2]

Description

Currently we have verify transaction, whether signature is correct or not, but we don't have a function to check if the schema itself is valid (without signature)

[tobiaslins]

@willclarktech
Want to throw something in here.
What about using ajv or joi for validation?
Will be much simpler then what you did on #678

https://github.com/hapijs/joi
https://github.com/epoberezkin/ajv

Not sure if it makes sense, but what do you think?

[willclarktech]

We'll revisit this for 1.1.0 and come up with a comprehensive solution for schema checks of all useful sorts. Thanks for the resources @tobiaslins, we'll check them out when we come back to this.

[willclarktech]

There's already enough in 1.1.0, we'll schedule this for 1.2.0. The plan is to use ajv.

[willclarktech]

Closed in #734