Add HTML report output for gaiatest

Add support for HTML report output for gaiatest.
To use this: just add option '--html-output=outputfile.html" after gaiatest cmd.

I didn't include the links to screen shot or html source in this version per Dave's comments 
"I would suggest enhancing the test results to include the raw debug data, this way the HTML report can be more self-contained. This may involve an enhancement to the Marionette test runner."

Also several js files need to be included in gaiatest install package. I modified setup.py to include this.