Fix scaffolding bug with Post.
Fix LoginController signIn action.
Sync chapters.
Update Grails wrapper to 2.3.7.
Sync up ch15 source.
Reorder chapters.
Remove unnecessary mock from PostServiceSpec.
Fix ch15 unit and integration tests.
Try to get tests working.
Sync ch16.
Fix ch16 source.
Fix ch17/hubbub-single.
Fix up single Gradle project.
Update build integration samples.
Sync ch18.
Update plugin to Grails 2.3.7.
Add ch20 code.