Now QUnit tests are working using GruntJS, and other changes

- QUnit tests are now in separate JavaScript files and all of them are
called from a test.html
- this.derived was declared on the $global.joopl.Object prototype. This
had no problems with modern browsers, but PhantomJS was crying. Now
this.derived is declared when a class is instantiated (same effect, but
it works on PhantomJS too!).