Adds scripts to test server under rapid requests, and to create a user

[DougReeder]

• The number of successful requests can be measured using npm run measure -- -o https://myhostname The "longest run length" is usually the most meaningful measurement.
• An pass/fail stress can be run using SERVER_URL=https://myhostname USERNAME=existinguser PASSWORD=iloveyou npm run stress-test
• Users can be created using npm run create-user <username> <password> if user creation is enabled.

This allows testing server configurations, to determine which is best for various loads. Also, some comparisons can be made of different backing stores.

Measurements will vary, depending on the state of the server, so multiple runs should be made. The absolute value of measurements is not important, only relative values.