convert burn rep to 2 dropdowns

i'd like to convert the 2.3 style of rep counting to 2 different fields to make the feature easier to use.

• add burn_set field to exercise_logs table
• validate burn_set only on update
• loop over each exercise log record and parse the existing data:

ExerciseLog.all.each do |log|
  if log.burn_set == nil
    if log.burn_rep == nil
      log.burn_set = 0
      log.burn_rep = 0
    else
      nums = log.burn_rep.to_s.split('.')
      log.burn_set = nums.first.to_i
      log.burn_rep = nums.last.to_i
      log.burn_rep = 10 if nums.last.to_i == 1
    end
    log.save
  end
end

• add dropdowns to the exercise_logs/form
• add new burn set & rep info to views & partials
• use JS to limit the set & rep dropdown options to the values that are in the log's form fields (on edit only)