release 1.9

• Comments
  • show comments and replies of step
  • post comments and replies with plain text
  • load more for comments and replies
  • autoupdate list of comments, when user post comment
  • LaTeX support for comments with optimization based on content of comment
  • empty states for comments
  • analytic for comments
  • material design fab for writing comments
  • support is_deleted = true
• fix wrong tab after recreating StepActivity
• fix bug with crash on null progress units
• fix matching quiz problem
• fix bugs