HOTFIX: Automatic Adcode Expiration Setting

AdCode Fixes.
1. Autocreated AdCodes now get an expiration date set automatically based on a setting
Setting is under the settings tab of the adcode list:



This is the number of days after creation before the automatically created adcode will expire

2. AdCodes are no longer immediately cleared from session when an order is placed

3. AdCodes should now be cleared from session when they expire, not only when the session expires AND the adcode expires, and when an adcode expires, a new session will be started.

These are aimed at fixing various adcode sales reporting issues and should hopefully help them to be more accurate. Previously, auto created adcodes would never expire by default, so that is a change in how these are handled.