Allow context variables on subject and message when processing alerts (FHCA-967)
When processing alerts is worthy to allow processing some context variables on client and system, for example to differentiate the system where the alert comes.
When running Alerts the server context has very few variables (it's a server context).
So, added the ability to put in the subject and message context variables refered to the client running the alert (AD_Client) or the system (AD_System).
Note that when using @Name@ in the alert subject it will replace it with AD_Client.Name.
To print the system name the following notation can be used: @AD_System_ID<AD_System.Name>@