consistent test results regardless of environment

[jelhan]

This ensures that CSP configured for test environment is always used regardless how the tests are executed (ember test, ember test --server, ember serve and opening http://localhost:4200/tests in a browser). It also removes some CSP only required for tests from the CSP meta tag in index.html if build includes tests and from CSP header used for serving index.html with ember serve.

Closes #119

[rwjblue]

Awesome, thank you!