Leads and Events views: add course marking lead

[louking]

• [x] lead table can have additional attributes "Finish Line", "Course Marking" - this will be hard-coded as they need to be displayed on the events page
• [x] add "active" attribute to lead record
• [x] remove Delete button from Leads view
• [x] display Finish Line Lead and Course Marking Lead on Events edit page
• [x] display Finish Line Lead and Course Marking Lead on Events table display (#209)