Add Codecov integration to CircleCI to track JS test coverage, with separate flags (#4219)

.travis.yml

@@ -78,7 +78,7 @@ script:
   tox
 
 after_success:
-  - codecov
+  - codecov -F backend
 
 # Who to notify about build results
 notifications:

circle.yml

@@ -17,3 +17,5 @@ test:
     - python -u runtests.py
     - npm run test:unit:coverage -- --runInBand
     - npm run dist
+  post:
+    - bash <(curl -s https://codecov.io/bash) -F frontend