Build: Change karma initialization strategy

* Add secure environment variables

* Instead of the "browsers" module use "launchers" to store
  browserstack browser launchers info and "environment" which
  would change karma settings for different environments
Build: Clean up

* Lint karma modules
* Prettify some statements
* Use "use strict" statement in karma modules
Docs: Reflect karma related changes in the readme
Build: Execute tests in Firefox from forks