Update Groovy DSL to support Liquibase 3.0.7

This pull request will update the groovy-liquibase project to the latest version of Liquibase, and it  fixes a couple of outstanding Issues:

1. The DSL now supports the latest version of Liquibase (Issue #38). As far as I can tell all new attributes have been added.  I've also added the new ```dropAllForeignKeyConstraints``` changeset.
2. I reverted the changes made to the ```include``` tag of a databaseChangeLog that was causing breaking behavior (Issue #37).  Reverting the change means we loose the ability to find changelogs in subdirectories or inside zip files, but more importantly, we regain the ability to process changelogs in the proper order.
3. There is a nasty bug in the way Liquibase calculates checksums on a ```sqlFile``` change set (Issue #36).  I reported the issue to the liquibase team (https://liquibase.jira.com/browse/CORE-1293), but since it hasn't been fixed yet, I've added a workaround to the groovy DSL.

I am also creating a pull request in the liquibase-plugin to use this DSL and fix some more outstanding issues there.  I'll make some testing comments there.