Update and add load testing scripts

[jwalgran]

There are 4 types of HTTP request activity that we want to be able to be able to simulate

• Loading the home page
• Zooming the map with a contributor filter
• Downloading a search result CSV
• POST a batch facilities API one at a time (mimicking a "bulk" upload from an API partner)

We need to be able to

• Run simulations of all 4 types of requests simultaneously
• Adjust the number of parallel virtual users making each type of request.