Add an initial db/schema.

This should allow CI to complete successfully, even though there aren't
any tests yet.
Merge pull request #3 from alphagov/add_db_Schema

Add an initial db/schema.
Entry model

www.agileplannerapp.com/boards/173808/cards/7897

An Entry stores the content_id, title, format and base_path
of a piece of content being edited in Publishing applications.

Ignoring the `state` attribute for now, because we need better
understanding of what's expected from that.

Making a couple of changes which remove warnings from test
output and ignore coverage reports in git.

Also, adding shoulda-matcher for consise validation specs.
Submit and fetch entries

www.agileplannerapp.com/boards/173808/cards/7897

the publishing applications use a content_id to
submit and Entry for a piece of content. for now
we need to retrive all entries for a particular
format.