Renames IssueStatus to Status
Adds migration
Moves controller action tests to specs
Moves done ratio update tests to specs
Renames done ratio update setting 'issue_field'
Adds changelog entry
Merge pull request #480 from opf/feature/migrate_issue_statuses_contoller_tests

[FEATURE] Migrate issue statuses contoller tests
travis likes it, jenkins likes it, apart from my personal dislike of excessive it_behaves_like-use no complains from my side.