Add add-platform, remove-platform, and list-platforms commands

Also, remove platforms from meteor add, remove, and list
Fix pluralization error in comment
Make changes requested by Arbesfeld, need to add tests
Update tests to match new command
Revert "Update tests to match new command"

This reverts commit 26145c5bd9e8ab58cb3b15f124f51d387831c81d.
Allegedly cleaned up failed refactor, pass all self tests