On item pages, fetch the item's library data to the store if it's not available

[mikiher]

This fixes #3209

The fix fixes the problem by making sure filterData is available in the store when the item page is loaded.

There might be some refactoring needed in libraries.js to make sure that dependent state variables are updated together. Currently for example, it is possible to change the currentLibraryId without trigerring a library fetch, which leaves the libraries state in an incosistent state (filterData is not updated, for example). Let me know what you think.

[advplyr]

The setCurrentLibrary calls shouldn't be happening so I replaced those. As far as I could tell the filterData should stay in sync.

I agree some refactoring can be helpful here.

• Collections and userPlaylists don't need to be loaded into state.
• There is still the old listeners setup in there that is used by LibraryTable.vue. Instead of listeners in the state it should be using socket events directly. Cleaner that way.
• Filter data in general feels hacky. I'm sure there is a better way to keep that refreshed and up-to-date. I don't have a specific solution off the top of my head.
• In the asyncData for all the library pages libraries/fetch is getting called every time instead of only when necessary.

As for this PR the issue is fixed. Thanks!