Update postfixadmin migration code

    Changes:
        - Update the code to actually work with the current version of
          modoboa.
        - Use database transaction to roll back if something goes wrong.
Merge pull request #577 from carragom/1.1.x

Update postfixadmin migration code
Migration script is now a regular management command.

see #577
Minor fixes in the pfxadmin migration script.

see #577
Domain/mailbox creation control when importing from LDAP.

see #591
Translation files updated.
Avoid backtrace display on domain conflict.

fix #591
Do not use translated content.

fix #598
Domain conflict check fixed.

see #591
New map file.

see #599
Merge branch '1.1.x'

Conflicts:
	modoboa/locale/cs_CZ/LC_MESSAGES/django.po
	modoboa/locale/de/LC_MESSAGES/django.po
	modoboa/locale/en/LC_MESSAGES/django.po
	modoboa/locale/es/LC_MESSAGES/django.po
	modoboa/locale/fr/LC_MESSAGES/django.po
	modoboa/locale/it/LC_MESSAGES/django.po
	modoboa/locale/nl_NL/LC_MESSAGES/django.po
	modoboa/locale/pt_PT/LC_MESSAGES/django.po
	modoboa/locale/ru/LC_MESSAGES/django.po
	modoboa/locale/sv/LC_MESSAGES/django.po