Users can view their package and edit the fields, including link names and URLs

Added links table and cleared out the link model
Use nested forms because a package has links and attachments on different tables

Features included:
Edit Content fields
Edit Links
Update via `Update Package` button
I know this could be better, but now sure how:

`generate` needs to return a `package` object.
`package.update(@email_adapter.data)` needs to go first because it saves the package, this giving it an `id` that both `update_links` and `update_attachments` use.
Since `update_links` and `update_attachments` are methods I made they just return true. Is the solution to have one of them return a package object, or keeping it at this level? It looks bad I know