Design enhancements; bugfixes

The categories' names in the screen management page how have a minimum
length of 1

Fixed a bug that caused potential integer overflow in the screen
management page

The filtering options in the screen management page have been enhanced
to display the filter's name and the number of results

Redesigned the CSS for the home page and the screen management page to
ensure compatibility with all screen sizes

Added shadows to top and bottom bars all over kPanel

Added hover coloring for the screens in screen management

Added better highlighting on hover on the database page

Enhanced the design of the content management page and made it
compatible with all screen sizes

Changed the way buttons appear and version is highlighted when hovered
over in the content management page in order to accommodate all screen
sizes

The content management page now retrieves the list of versions through
POST as opposed to using cookies