Changed 'cozy' to 'cozy-dev' and fixed readme accordingly

I made the modification accordingly to our discussion this thursday. Repo's name should also be changed (see the internal email).

I have changed things to make the NPM package's name to be "cozy-dev" too but I'm not too sure of:
* it's feasible to do that in NPM
* it's something we actually want ('cozy' would be free to take)

Let me know if I must change a anything.