Allow configuration from the gruntfile.js

This pull is to allow users to enter configuration directly in the gruntfile.

example : 
_gruntfile.js_
```
// Configuration to be run (and then tested).
    protractor: {
      options: {
        keepAlive: false
      },
      test1: {
        baseUrl: 'http://localhost:4100/app/',
        configFile:"test/protractor-conf.js"
      },
      test2: {
        baseUrl: 'http://localhost:8000/app/',
        configFile:"test/protractor-conf.js"
      }
    }
```

This is already available with grunt-karma-runner and would be great to have available in grunt-protractor-runner.