test(pageObjects): Added rxEnvironment Page Object

Added a page object for rxEnvironment. getEnv returns the current environment.
As far as testing this functionality is concerned, you won't be able to visit anything that matches these environments exactly in the encore-ui project's demo page. This opens up some good opportunities to exposing the `environments` var to users, including *this* project for tests.

I'm actually going to just push up a commit in my fork and link to it here so you can get an idea of what I mean.