rake task for db setup

In this PR:

1. Add db groups. 

2. Rake task. Init db setup can be automatic. Here are new steps to init db.
  *  Copy "config/database.yml.template.[YOUR_DB]" to "config/database.yml". Or configure the "database.yml" by your own settings. (Since the file "database.yml" is private, it should be ignored by git)
  * Run command: "rake db_setup". The command will load info in the "database.yml" file and create dev db, testing db, tables, and load seed data.

3. Upgrade rails and add some new gems to facilitate developments