Grunt task

Adds a grunt task at `grunt/internTask.js`. 

**Example configuration showing all options**

```js
grunt.initConfig({
    intern: {
        someReleaseTarget: {
            runType: 'runner',  // defaults to client,
            options: {
                config: "intern-selftest/tests/selftest.intern.js",
                reporters: ['console', 'lcov'],
                suites: ['intern-selftest/tests/all'],
                proxyOnly: true,
                autoRun: true
            }
        },
        anotherReleaseTarget: { ... }
    }
});
...
grunt.loadTasks('path/to/intern/grunt');
```