Revert old OModel classes and enhanced migration

Reset all changes of old OModel classes.
Enhance object model migration support so that old persisted object models (without extension activity support) can be migrated to the new object model.
Changed GEMFILE so that a fixed version of buildr (1.5.3) is used due to some problems with buildr version 1.5.5.
Reset .gitignore file.
10 files changed