Import modules by new names

Use new module names to import from email and migrate packages, to fix pylint 'no-name-in-module' error.

This will drop support for email package version 3 and older. I don't think it should be a problem, as email 4.0 is distributed with python 2.5 release. (http://docs.python.org/2/library/email#package-history)

This pull request also removes code need to use sqlalcheny-migrate package 0.6.1, which is officially no longer supported by buildbot.

I'm not enabling pylint no-name-in-module check yet, as there is still other error reports that need to be fixed.