Add a toggleable button for showing or hiding indirect mods. By default
indirect mods are not shown. Indirect mods are installed as child mods from a
top-level mod, and most of the time the setting screens are not relevant for
those.
Add a search/filter widget to hide non-matching mods. This is useful when you
have a lot of mods installed. By typing a few characters, only mods with a
matching name or id will be shown.
Solves #10 and #12.