round-off weight value while returing grading policy

TNL-884
@waheedahmed @mlkwaqas @adampalay 
Fix issue where when a user tries to set weight to some specific value e.g, '29' then 'jsonize_grader' method returns it as floating point '28.999999999999996' and displaying it on front end gives '28' instead of '29'
I'd just add a comment explaining why you're rounding here. Also, are 2 decimals enough? Is it possible to change the rounding on the front end, rather than the back?