Add support for controlling API url in UI without modifying code.
Add support for controlling API url in UI without modifying code.

Reviewed at https://reviews.apache.org/r/63040/

medallia/aurora,thinker0/aurora,thinker0/aurora,apache/aurora,rdelval/aurora,thinker0/aurora,apache/aurora,medallia/aurora,crashlytics/aurora,crashlytics/aurora,apache/aurora,medallia/aurora,crashlytics/aurora,thinker0/aurora,rdelval/aurora,medallia/aurora,apache/aurora,apache/aurora,thinker0/aurora,rdelval/aurora,medallia/aurora,medallia/aurora,rdelval/aurora,apache/aurora,crashlytics/aurora,crashlytics/aurora,rdelval/aurora,crashlytics/aurora,thinker0/aurora,rdelval/aurora