Assignment 3 - Part 3

The USERS page now displays a list of all members in a table and allows
a logged in user to challenge a member to a game of checkers.

Other changes:
- In preparation for part 4, all checkerboard related scripts were moved
to an external file
- Moved the checkerboard to the new GAME page (part 4)
- Simplified the code by removing client-side form validation scripts
made redundant by html input controls and server-side validation

Improvements needed:
- Need to modify the way the sidebar and main content areas are
displayed so that they can automatically grow or shrink according to the
amount of content
- Need some random content to replace the checkerboard on the HOME page