Implemented display of Category Hierarchy in Categories dropdown

- Refactored JS to assign depth levels to each Category.
- Added CSS classes for visual representation of Categories Hierarchy.
Implemented display of Category Hierarchy in Categories dropdown

- Refactored JS to assign depth levels to each Category.
- Added CSS classes for visual representation of Categories Hierarchy.
Merge pull request #1 from daigo75/master

Implemented display of Category Hierarchy in Categories dropdown