test(pageObjects): Added rxEnvironment Page Object

Added a page object for rxEnvironment. getEnv returns the current environment.
I was originally going to doing it this way. I decided not to since it'd decrease the dryness of the code.

Also, see https://github.com/rackerlabs/encore-ui/blob/f91ca82c3d4647de50a24b31077722bf75feacf7/src/rxSortableColumn/docs/rxSortableColumn.midway.js#L28-L32.

This needs to addressed in better ways, I think.