Add default app theme to sc-init and sc-gen app

[ialexi]

sc-init/sc-gen app should be changed in the following ways:

• Each app should have a buildfile with config :app_name, :css_theme => "ace.my-app"

• Each app should have a theme.js file creating a theme for the app. Something like this, but with appropriate comments:

  MyApp.Theme = SC.AceTheme.create({ name: 'my-app' });

  SC.Theme.addTheme(MyApp.Theme); SC.defaultTheme = 'my-app';

[ialexi]

Done.