Add filters_spam attribute

fix @spam_count test in view, add dependency to gemspec
Add test for marking as spam/ham
Fix bug in test with Actions
Fix mark as spam
New tests for the Show and Action links
Login before tests
Stop tests failing if spam is switched off
Remove trailing whitespace
Correct the bad "before" block in spec
Use route helper for the "back to all" path
Create an item for the show test
Correct renaming of confirmation_body to _message
Fix @includes_spam to include_spam?
Mark as ham/spam specs