In the future, removing exports is likely going to be a feature. Handle
the case where the export data is removed from a mod pack in the locale
and prototype metadata stores.
If the unsubscribe function is called multiple times the indexOf
function will return -1 which will end up removing random other
subscription callbacks. Prevent the incorrect callabck removial
in this case.
The handling of exported data such as locales and icons in web_ui was
based on a model where there is only one set of data exported per
cluster. This model changed to have one set of exports per mod pack
when mod packs were introduced, but the existing web_ui code was
bodged to use exports from a "default mod pack" on the controller.
Refactor the code loading exported data to take the mod pack as an
argument for selecting which exported data to load. The different kinds
of prototype metadata that can be loaded is consolidated into one
`useExportPrototypeMetadata` hook. The logic for displaying icons is
put into a `FactorioIcon` component. And the obsolete
`useExportManifest` hook is removed.
These changes allow the `/icon-reference` page to display exports on a
per mod pack basis. Which has now been linked on the bottom of the mod
pack view page.
Hornwitser