Implement level labels

[Toastbrot236]

This implements:

• An enum containing hopefully all labels, aswell as some methods to (de)serialize them for the game
• The ability for publishers to set up to 5 labels for their levels
• The ability to filter levels by publisher labels in-game
• Migrates review labels to be stored using List<Label> instead of string
• Adds some label sanitization
• When level statistics get recalculated, the 5 most recurring labels among a level's reviews get saved in its statistics to have them show under levels in-game aswell (the game differenciates between publisher and non-publisher labels there)
• Deduplicates code used by both tags and labels
• Fixes tags to show up on levels in-game again