Dopr attachments_email_templates join table

[#51985479]

Mdm::Attachment and Mdm::EmailTemplate no longer exist, so no need for a
join table between them.
Drop attachments table

[#51985479]

Drops attachments table that is no longer needed because
Mdm::Attachments no longer exists.
Drop email_addresses

[#51985479]

The email_addresses table was used by the old-style campaign model
Mdm::EmailAddress, which is no longer defined, so the table can be
removed.
Drop email_templates

[#51985479]
Drop web_templates

[#51985479]
Drop campaigns

[#51985479]
Bump version number.

[#51985479]

Increment PATCH number since tables should have been deleted when models
were removed (and MINOR was incremented), so it's only a bug fix to remove the tables.
Merge pull request #31 from rapid7/bug/obsolete-campaign-tables

Drop obsolete campaign tables