[WIP] Rework Build Script

So I've been talking with our API guys about some rate-limiting I've been experiencing when running tests.

They recommend that I switch over to using an OAuth application and token - which allows for higher 

- [x] introduce Powershell script because it allows for better scripting of environment
- [x] add `set-credentials.ps1` helper script for populating credentials and client id/secret
- [x] switch integration tests over to use token (if it exists)
- [ ] update documentation to explain these changes 
- [ ] validate token and, if not valid, get a fresh token and set it before running tests

![screen shot 2013-12-26 at 1 22 57 pm](https://f.cloud.github.com/assets/359239/1809345/e30d4b0c-6dd8-11e3-8284-d82b0e23dd12.png)

Test Plan:
 - [ ] no environment variables - see warning message about credentials, no integration tests
 - [x] existing username/password environment variables - see warning message about new credentials, use Basic authentication for integration tests
 - [ ] valid token found - no warning message, use token for tests
 - [ ] invalid token found - no warning message, message about updating token, use new token for tests