`self.janitor:add(Janitor.new(), "destroy")` memory leaks

Occurences of:
```lua
self.janitor:add(Janitor.new(), "destroy")
```
are memory leaks if once the inner janitor is destroyed it doesn't get removed from the outer janitor.

They need the following pattern:
```lua
local janitor, objectIndex = self.janitor:add(Janitor.new(), "destroy")
janitor:add(function()
    self.janitor:remove(objectIndex)
end)
```