Better Javascript loaders support: files to be loaded can be read from configuration

When using a Javascript loader (e.g. requirejs), the [setup guide](http://jaketrent.com/post/test-requirejs-testacular/) states that it is necessary to maintain the list of test files:

> Require Each Test File
> 
> One of the things I hate is having to update a master list of all tests to run every time I add a test. Unfortunately, that’s what I currently have. The test main module has to specifically require each of the test modules. I would love it if I could add a *.test.js file to the test directory and just have it run the next time the tests run.
```

This pull request contains code to avoid this. Files can be specified in the configuration with:
```
{pattern: 'test/**/*.test.js', included: "requirejs"}
```

And they will be automatically loaded by the requirejs adapter.
Adapters for other Javascript loaders can also benefit from this feature.