Add a filter type for the module install state

We do have the 'Installed ☑" in the lower right. Is that not enough?

What would the UI be for this, by the way?

Single checkbox: "[ ] Show installed only"

3-way radio:
(o) Installed ( ) Uninstalled ( ) Any

Something like this is most consistent... ?

This is a really interesting problem. While adding an additional filter is one solution to this problem, I wonder if ensuring that non-installed modules populate to the top of the search results is a simpler solution. An example of this pattern is similar to what exists in applications like Grubhub (where restaurants that are open populate to the top).