Initial database work.

Add User model. Database migrations after a few iterations. Fix missing
`irbtools'. Add corresponding tests.
Done with User mode (including passwords)

End of chapter 6 we've implemented user models and password
authentication.
End of Chapter 6

Changed the regexp that validates emails (got it from RI), suppress
pending tests, tests email downcasing and saving the original email
format the user entered.
Merge branch 'modeling-users'

Bring all the work from Chapter 6 to master branch.