[gh-618] Upgrade Drupal Core to 7.20
[gh-621] Ignore liferay calendars during migration.
[gh-623] Create a drush command that can run the migration tool.
Merge pull request #619 from tsteiner2/issue-618

Closes #618.
Merge pull request #622 from tsteiner2/issue-621

Closes #621
Merge pull request #624 from tsteiner2/issue-623

Closes #623