Add delete functionality and confirm destroy method
Functional and integration tests added for delete mechanism
Routes for 'confirm delete' page and actual destroy action

Destroy and confirm destroy functionality
PopularLinksEdition.can_delete? method to test if edition can be deleted
Tests for confirmation page and cancel delete

Tests for:
 Show previously published edition
 Successful and unsuccessful delete from DB

Application error message was being used twice, so extracted out to own method.

Added an extra check to ensure that there is no way to delete a published edition.
To prevent issues with multiple users accessing the same edition.

Link renamed to 'Delete draft'
Application error message makes it clear that it was a draft that failed to be deleted not an edition
'Can't delete published edition' message updated to be more helpful
Confirmation and success messages reworded to be clear it is a draft that will be/has been deleted

…e of error message method

Fixed incorrect test title
Fixup! Add missing test and extracted error message method
Rename of error message method
Removed content block that doesn't exist in mainstream

Improved test - more descriptive name and added assert for the error message
Test improvements - more accurate names and extra assert
Renamed tests to more explanatory names
Added test to check alert and redirect if delete from DB fails with an exception
Divided tests into 3 contexts - 'draft', 'published' and 'database errors'
Moved context blocks 'destroy' and 'confirm destroy' to after 'publish'
Moved the test for deletion failure to #destroy #draft context block
Added redirect assert to test for can't delete published edition