[Feature Request] Add config switch for sign editing

[Fourmisain]

There are multiple reasons why one might want to disable sign editing:

• Conflicts with other mods (e.g. Better Signs & Frames)
• Wanting to use another mod for that feature (e.g. Edit Signs)
• Wanting to disallow sign editing on multiplayer servers (e.g. using Flan) or in Adventure mode - normally if you can't break the block, you can't change the sign, but sign editing circumvents that