Implement Grunt support (grunt jshint,csslint,qunit,watch)

This has no influence on Jenkins but can be used locally to
easily run certain tools. Since we already had `.jshintrc` in
our repo it was already possible to easily run JSHint from
the command-line locally. Taking that as a base the following
are new features:
* `grunt csslint`: Runs CSSLint on all css files
* `grunt qunit`: Runs QUnit (standalone) tests in PhantomJS
* `grunt test`: Runs jshint/csslint/qunit
* `grunt watch`: Runs the "test" command automatically whenever
  a file is changed. You can keep this in the background so
  whenever you save a file in your editor (e.g. Sublime Text)
  it'll run the tests and if there is a failure, it'll throw a
  bash error code causing your Terminal application to beep you
  in whatever way your operating system does so (e.g. for
  Mac OS X a red badge + jumping icon in the Dock). It will
  continue to run in the background even after a failure so no
  need to re-start watch after a failure.
* `grunt`: Runs the default task, which is 'test'.

Previously to use `jshint .` you had to:
* One-time install:
  * install package -- nodejs npm
  * npm install -g jshint
* Usage:
  * cd VisualEditor; jshint .

Now, for grunt:
* One-time install:
  * install package -- nodejs npm
  * npm install -g grunt-cli
  * cd VisualEditor; npm install
* Usage:
  * cd VisualEditor; grunt

Change-Id: I7a4fdf4b6bf3f00cef15dc3e2c81eceb595aec7c
Merge "Implement Grunt support (grunt jshint,csslint,qunit,watch)"