Implement toString method in base transaction class

[rainydio]

Current Behavior

Most log lines only include transaction id. It's difficult to understand what exactly is going on.

Expected Behavior

Human-friendly description may include sender address, nonce, transaction type, and some type-specific fields.

Possible Solution

Implement toString method in base transaction class.

Context

When tests are executed pool is generating a lot of log lines. But it's difficult to read them and debug if something goes wrong.

[rainydio]

Merged