Add draft for filtering design

This is a proposal how to do filtering of a system description in Machinery. Feedback is appreciated. Please add it as comments in this pull request.

How would one apply multiple filters? Specifying multiple `--filter` options? (In other commands we decided to not use multiple options but combine them into a comma separated list instead, e.g. for the scope list, but that won't work that easily in this case because of the comma sparated lists inside of the filters.)