NixManager Plugin

Please review my BackEnd code, there is no UI implemented yet only unit tests. but BackEnd is complete and making UI will be much easier then debugging CPP code at runtime which runs shell commands.

There is a lot of code so I will like to request one very simple rule: if you propose a change of more then 50L or rewriting a function please make sure it passes the unit tests.

There is a documentation file in the source code.

It outlines how to talk with BackEnd from GUI perspective, in general I'm a heavy commenter so please consult header files for briefs about what the function does.

I would like to direct attention at my failed attempt to copy the implementation of the other plugins of getting the plugin Icon to load in Settings, because I couldn't figure it out and I'm probably being dumb about it.

This is probably the start of many drafts but I'd like to get the process started now.