CRM-13630 fix - Minimum contribution amount check for Premiums fails whe...

Its hardcoding this time - reason of which it perfectly works when we use manual membership type options instead of existing membership type price-set as in later case the id changes to ".{Price-set name}-content" instead of ".contribution_amount-content" in former case. To avoid this dependency "#priceset" class is being used and it is acting on premium smoothly. This issue also persist in case of using existing Contribution type price-set for the same reason mentioned (check the diff). 
         In addition in case of 'other contribution amount/without price-set' no changes required as the id doesn't change.