Add a "TEST" indicator to test instances

[avishkar58]

trafficstars

Currently the test and production instances of baobab look identical (eg test-baobab.deeplearningindaba.com and baobab.deeplearningindaba.com) - this can make it difficult to spot issues like someone being on the incorrect instance. Add a red banner/indicator/pill/something to test instances in the middle of the top menu bar to indicate that it's a test instance. Some options for identifying that it's a test instance:

• Inspect the organisation's system_url or the REACT_APP_URL for the word "test" in the URL (not very robust)
• Add a test flag to the organisation model, return it from the backend API and use this in the front-end.