Added support to compile using Docker

[attrib]

While working on #608 I needed a way to run unit tests and build the lib.

On my working machine I didn't wanted to install grunt-cli and bower.

Because I'm a big fan of Docker I created a Dockerfile and minor documentation in the README how to use it.

Just wanted to share this as I did this now anyway.

After running the commands, the compiled output is created under dist like grunt would do it normally. You just do not have the other folder hanging around like node_modules, ect.

Merge request checklist

• [x] I read the guidelines for contributing
• [x] I created my branch from dev and I am issuing the PR to dev
• [x] Unit tests are OK
• [x] If it's a new feature, I added the necessary unit tests
• [x] If it's a new language, I filled the __locale and __author fields