JS-T: META: Centralization of testnet tutorial accounts & keys

[relativityboy]

This tutorial builds on #113. While the data-flow was good, the browser fetch process, data-structure, and file locations looked like they'd add code complexity to individual tutorials.

• As a tutorial maintainer, I want an easy place to link to for "more" testnet "play" accounts in both the readme, and in the active tutorial code.
• As a tutorial user, I want to have options if the default accounts for a tutorial have been hijacked.

AC

• [x] a standardized location in this repo for testnet accounts with account names & priv keys
• [x] a file that is importable from our tutorials, or a plan for making an importable file.
• [ ] explanation of what was decided & why in # Result/s comment

[relativityboy]

Results

Decided to place a configuration file within the tutorials directory, and have it be a standard .js file for easy maintenance (fewer ") and flexibility (we can update the structure of the file so that only the account, or item needing to be imported will be.

We chose to rely on a compile-time import (as compared with an onload event network request A-la #113) to make the webpack configuration and the tutorial boiler-plate both little simpler and easier to maintain.