DRY SpecialistDocument show views
DRY SpecialistDocument index views
DRY SpecialistDocument new & edit views
DRY up form errors into a shared partial
DRY attachments forms for specialist documents
DRY up common form partials for js preview

We also DRY up the path helpers for new and persisted previews. This involves a slight change to the path for new previews. As rails by default checks persisted to decide wether to build the path on the collection or as a member, I have pluralised the new paths. This matches closer to rails' standards.
Merge pull request #228 from alphagov/refactor/dry-specialist-document-views

Refactor/dry specialist document views
Add Drug Safety Alerts schema
Add model, builder and validator for DSA
Add Drug Safety Alerts to Wiring
Add formatters for DSA
Permission check for DSA for MHRA editors
Add controllers for DSA
Add observers and services for DSA
Adding view for DSA