Comment Functionality + Post Detail UI

[githelsui]

• Scrollview... with 3 stackviews
• [x] UI with stackview for post detail:
  • stackview 1: post
  • stackview 2: post stats
  • stackview 3: comment section
• [x] Comment Section Stackview
  • at most 2 commentView subviews (consist of a horizontal stackview) ~ hide subviews until comments exist for post ~
  • always show button at bottom of commentViews
• [x] Create Comment custom PFObject
• [x] Query Comment class for that post
• [x] 'Leave a Comment' button leads to modal view
• [x] Update post cell with comment count
• [x] Update post detail with comment count