Add a few Substitution formulas

Nicolas CHIGROS

Add a few Substitution formulas:

• Substitution formulas @computername equivalent to %computername%
• Substitution formulas @userrole matching the user role
• Substitution formulas @userdisplayname matching the user display name
• 
  Substitution formulas @timestamp matching %timestamp% that is culture insensitive (unlike @datetime)

Last two use case is when you need to log when a user launched a process using a procedure more cleanly.

First one would be use fully to do thing like change a background color to warn user they are in Qualification or development server.