Rebuild Item Names Database slow and never resets

[sliekens]

The button that lets you rebuild the item names database only starts rebuilding the database the first time that it is pressed. This is because the RebuildItemDatabase(...) method is invoked by the constructor of the RebuildNamesDatabaseViewModel, and the viewmodel is only instantiated once for the lifetime of the application.

Besides that, the entire process is kinda slow and could be sped up by using the paginated items endpoint and by handling tasks asynchronously.

[SamHurne]

Funny, I was just noticing this myself...

See commits 8bcf466, e2bacc8, and 423777d.

[sliekens]

I'd like to propose a cleaner solution than what you added in 8bcf466