refactor(server): follow recommended project layout, put server in bin

- Put server in bin folder
- See [this
post](http://stackoverflow.com/questions/22380293/recommended-dart-proje
ct-layout-for-public-private-app-server-and-or-test-fil/22380294#2238029
4) for details.
refactor(recipe): make .fromJson() a generative constructor

Make `Recipe.fromJson()` a generative constructor instead of a factory.
Merge pull request #103 from chalin/patch-0313-server-in-bin

refactor(server): follow recommended project layout, put server in bin
Merge pull request #104 from chalin/patch-0313-recipe-not-factory

refactor(recipe): make .fromJson() a generative constructor