Minimum length change for user first and last names on registration form

This fix is for issue #76: "Define a minimal number of characters for users' name and last name". 

Notes:
The minimum length of the first and last name fields has been hard coded to 2 characters. A better solution would be to allow admin users to update these values without having to compile the code again. Ideally at some point in the future these values would be placed in a central config file or read from the database.