Feature/gbr 41

This is a pull request for https://github.com/caitp/grunt-bower-release/issues/41

It has a number of Git repo files committed inside the ```test/e2/``` folder. 

Indeed, there are end-to-end tests for new functionality, as well, as a regression test. Unlike previous tests, which are still there, they don't rely upon ```grunt test```, instead they can be run using nodeunit. I, for example, can run them using WebStorm.

The way those test work - each of them has a resource folder with a Gruntfile.js. Some of the tests create a git repo on the fly and check whether it contains a newly pushed tag. Other tests has already a git repo with all the necessary tests pre-conditions.