Deleted ProjectRequirement model; refactoring Requirement model to reference Project model.
Moved TimeStampedModel to projects app since Requirement model now has dependency on projects app.
Added slug and project field to Requirement model.
Only display text and tags fields when adding Requirement to keep form simple.
Updated RequirementListView and RequirementCreateView after adding slug and project fields to Requirement model.
Added add button to requirement_list template.
Included requirement.urls when /r/ is matched.