Add 'restart' and 'console' tasks. Stop nginx gracefully

On my machine nginx workers are not killed when the master process is (I
think the wrong signal is sent). Fortunately nginx allows to stop a
running instance gracefully (see http://wiki.nginx.org/CommandLine#Stopping_or_Restarting_Nginx)
Merge pull request #4 from pauldub/feature/rakefile_improvements

Add 'restart' and 'console' rake tasks. Stop nginx gracefully by @pauldub