Ignore creating tables, if they already exist

[chrispelzer]

Wrap the creates with hasTable to make sure they don't exist before trying to create them, otherwise it will error if tables are created outside migrations with no way of avoiding previously

Fixes #67

[webcodecs]

I would recommend to wrap the publishing of the migrations with hasTable and not the migration himself. In this case we will get a lot of entries in the migration table.