(thoughts): more readable transaction flow

[danwbyrne]

After working on #2096 its become apparent to me that our transaction flow for creating, signing, verifying, and sending is decently difficult to follow and debug. Whether that is because of my own mediocrity is up in the air but when I used neon-js to help debug our invocation transaction structure I found that there code was abstracted in a very legible way that allowed me to make only a few changes to grab the transaction object when I needed it. You can see that here and compare it to our code here

I think we should consider formatting our Client / AccountProvider in a way that better isolates the different steps of creating a transaction in our upcoming changes for 3.x