Add definition of "COMPLUS" to the glossary

Add definition of "COMPLUS" to the glossary

In the same vein as "COR" and "URT", the terms "COM+"/"COMPLUS" appear frequently throughout the codebase, most notably in config settings (e.g. "COMPLUS_DefaultVersion"). I couldn't find any other explanation for what this means, and since I remember learning about it myself by asking older members of the team, I thought it would be helpful to have this documented for newcomers to the codebase.