Create additional environment for testing

[jonrkarr]

I added separate configurations for test and development environments

• .env: production environment -- api.datanator.info
• .env.test: test environment -- testapi.datanator.info
• .env.development: development environment -- testapi.datanator.info

Locally, the default environment is development.

In CircleCI the environments will be used as follows:

• master branch: production
• other branches: test

[jonrkarr]

The one thing left is to change the REST API locations for the test and development environments to HTTPs (#254).