Replaced all instances of KID with DID (Issue #28)

Replaced all instances of KID in the modified key module code with DID.
Replaced every instance of "Key" with "Discount" (Issue #28)

Replaced every instance of the word "Key" with "Discount" in the copied
"Key" module code.
Replaced all instances of $K with $D (Issue #28)

Replaced al instances of the $K variable with $D in the copied "Key"
module code to be used to create the "Discount" module.
Updated Discount module revision numbers (Issue #28)

Updated revision numbers and disabled old code for handling out of date
modules.
Added "Discounts" module to config.sample.inc.php

Added "Discounts" to module configuration section of
config.sample.inc.php.
Fixed issue displaying and accessing training and discount modules (Issues:  21, 27, 28)

Figured out why new modules weren't displaying.  Damn pluralizations.
Sacrificed proper grammar for functionality. "Trainings" it is.