Improve `cabal init` defaults

Many users, including myself, get frustrated when starting a new project. The `cabal init` experience is very pleasant, but the defaults for packages and the generated code could be more practical:
1. `cabal init` should include various important packages in the default project (such as `text`, `containers`, `bytestring`)
2. ideally, the generated `Main.hs` should use some of these packages, so that there are as few "unused package" errors as possible
3. the library should generate more than one file, in order to show how to have multiple files in a cabal package
4. should the generated test file include some logic?

Is (1) possible? If so, we can come up with some more specific ideas for (2,3,4)