New global event: OnSave

[ramon-bernardo]

Pull Request Prelude

• [x] I have followed proper The Forgotten Server code styling.
• [x] I have read and understood the contribution guidelines before making this PR.
• [x] I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

• Add new global event: On Save.

Why don't we call in saveGameState? In situations like shutdown, things happen beforehand (players being sent off, etc.), so we call individually.