removing unwanted controllers
Caching, Refactoring, UI updates

- Added a top level controller to make rendering pages easier. As all
our pages have the same template. You can pass the main content view to
this function.
- Enabled database caching for caching categories.
- Added categories dropdown in the header to browse parts by category
- Modified part listing page to display category name at the top and
some other minor UI tweaks
Bug Fixes

- Items were not being added to the cart while browsing by category.
- Moved the add to cart code to a function and called it both the times
- Cart controller was not using the new rendering function from the top
level controller as a result the categories were not loaded in the
header
- Removed unwanted css from the header