Migrate all icon URLs to blizzard links

[Nakroma]

I'm submitting a...

• Bug report
• Feature request
• Documentation issue or request

Current behavior

Currently the raw icon name is used in the item database and the wowhead link is added manually.

Expected behavior

This needs to be migrated so that the item database uses the official blizzard link by default (see here: https://github.com/nexus-devs/wow-classic-items). Might also make sense to keep the icon prop and define an imgUrl property for the actual url.

Minimal reproduction of the problem

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Additional Description