localhost color theme

[bearzk]

Overview

When the app is running in local, it uses a purple color theme.

Testing recommendations

start the app locally and we should see:

also added a test file for the env detection util function.

GitHub issue number

Fixes #1466

Checklist

• Code is written and works correctly;
• Changes are covered by tests;
• Documentation reflects the changes;
• Update rebar.config.script with the correct tag once a new Fauxton release is made