Hiepluong dev request

Previous updates:
- Validation for empty name
- Drag drop for ordering (position)
- Separated Operation for Display student level and Achievement

additional updates:
- add id for li tags of nav bar, add span wrapper around the name of the sidebar item
- put ajax url into hidden field
- using function of javascript object data.success_func(result) and get rid of if else chunk
- using update_attributes(..) and get rid of case when statement
Consider using https://github.com/swanandp/acts_as_list. Otherwise, this logic should also be encapsulated in the model. 

In terms of MVC, we always aim for THIN controllers and FAT models, where more logic go into models, and if models grow too fat, to extract logic out into special Service objects.