Add Docker build.

Results are cached for optimized performance:

bash-3.2$ docker build -t cosminonnet/express-4-angular .
Sending build context to Docker daemon 3.021 MB
Sending build context to Docker daemon
Step 0 : FROM dockerfile/nodejs
 ---> 3c66918dcfc0
Step 1 : WORKDIR /var/web
 ---> Using cache
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Step 2 : RUN apt-get update &&     apt-get install -y git git-core &&     npm install -g bower grunt-cli
 ---> Using cache
 ---> 0272523b40eb
Step 3 : ADD package.json /var/web/package.json
 ---> Using cache
 ---> 3ada01c67328
Step 4 : RUN npm install
 ---> Using cache
 ---> 019fe8245941
Step 5 : ADD .bowerrc /var/web/.bowerrc
 ---> Using cache
 ---> 404cb6a5b50c
Step 6 : ADD bower.json /var/web/bower.json
 ---> Using cache
 ---> 0fd036aa2d53
Step 7 : RUN bower install --config.interactive=false --allow-root
 ---> Using cache
 ---> 6d6c9d508104
Step 8 : ADD . /var/web
 ---> Using cache
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Step 9 : RUN grunt build
 ---> Using cache
 ---> f7e979fe716c
Step 10 : EXPOSE  3000
 ---> Using cache
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Step 11 : CMD ["node", "server.js"]
 ---> Using cache
 ---> 1d73fd50961d
Successfully built 1d73fd50961d