Adds a makefile

I always had to look up the steps to get the hifis-net development server up and running on my local machine. So I set up this Makefile which will do all the tasks for the lazy developer.

To get the whole thing running, including installation, submodule update and jumbotron generation, run

make all

The steps can also be started individually:

make install     # install dependencies and update submodule
make jumbotrons  # build the jumbotrons using ffmpeg
make serve       # start the dev server
make clean       # Remove all generated/downloaded files

The steps are also documented in the README.md.

I could not find an easy rule for only building the jumbotrons when it is required. If there is someone who has an idea, please feel free to contribute :)