Adding support for collecting JS CodeCoverage with blanket.

UncoveringTheBlanket - Disabling blanket when running tests from command line.
    
When running tests from command line blanket has to be disabled otherwise QUnit.Start() will be called twice which causes a "global failure". Note that chutzpah has an option (/coverage switch) to collect code coverage and is using blanket (sic!) to do this.

Added blanket.js for JS code coverage
    
    Resolves #1625