Some ideas on improvements to the engine code

Here are the things I went for:

- Yehuda says: don't check in your Gemfile.lock yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/ :)
- Remove some unused stuff left over from engine generation
- Trim the migrations: by pushing the migrations together you create less bloat in the user's codebase

Cheers!