fix(karma): Fix Travis being unable to authenticate with SauceLabs

* Set the username & authentication key to the secure TravisCI env variables
* Steal the good parts of the AngularJS karma config:
  * Output the debug log into a file that's printed to the console a the end
    of a test run.
  * Set Travis specific config settings if the environment is Travis
  * Set startConnect to 'true' on local
  * Removed username and auth key values from karma.conf.js - will search for
    and use the local environment variable instead.
  * The specificOptions variable allows for custom values to be passed to
    certain configurable variables. More flexibility will be added over time.

BREAKING CHANGE: Other devs will need to use their own OpenSauce/SauceLabs
credentials to run SauceLabs tests from their local machine. Carry out the first
step of the Node.js tutorial (creatin g your own environment variables) as seen
here:
https://docs.saucelabs.com/tutorials/node-js/
*By successfully running npm install you will already have the necessary tools
 to connect to saucelabs.