Add minified version via Grunt/UglifyJS

Here we go with the pull request to issue #219 

## Changes

* Add grunt and needed plugins for minifying
* Add Gruntfile to configure minifying
* Add minified file and sourcemap to bower package
* Add info about installation of dev dependencies to README
* Add minified version and sourcemap to version control

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It would be a nice addition to fire the tests from the command line via `npm test`. But I guess that should be handled via a separate pull request :octocat: