Better setup

While I was setting up the app in my development machine, I found a few things that could be better in the setup process. Some external dependencies were not checked before actually installing gems, and the process of having to run the `setup` script at least twice (see https://github.com/elm-city-craftworks/rails_setup/pull/4) felt weird to me.

### Changes

* Added some colors for prettier error messages.

![screen shot 2013-05-22 at 12 45 41 am](https://f.cloud.github.com/assets/613784/564278/f2dd4838-c550-11e2-9d27-e3450a4818eb.png)

* Check for Ruby 1.9.3

![screen shot 2013-05-25 at 12 41 31 pm](https://f.cloud.github.com/assets/613784/564280/2a589a92-c551-11e2-9f9c-48ba581672d9.png)

* Check for PostgreSQL since setup will fail if you don't have it properly installed.

![screen shot 2013-05-22 at 1 04 43 am](https://f.cloud.github.com/assets/613784/564281/3dec3924-c551-11e2-861d-0bff407a3a91.png)

* Check that you have `bundler` gem installed

![screen shot 2013-05-22 at 2 34 02 am](https://f.cloud.github.com/assets/613784/564282/489096f4-c551-11e2-9e19-91b55b6f9b1f.png)

I also made some general small refactorings in `bin/setup` and `lib/tasks/setup.rake` files.

Any feedback is appreciated! :smile: