Create mechanism to manage the opDB update

opDB schema is defined by `model.py` and a new database can be created by using this definition. Currently, however, there is no mechanism to update the existing opDB with records when this schema definition is updated, which happens frequently. The procedure is (semi-) automated if possible. 

Database migration tools (such as alembic) are options, but we may like easier and simpler way. Anyway, we should start from finding out what kind of options we have for this purpose.

Furthermore, we like to manage the installation of the opDB package through `eups`.