Clean up cached party/guild data when leaving/disbanding

[MishimaHaruna]

Pull Request Prelude

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

Changes Proposed

1. Clear the party ID from the saved character data, when leaving or getting kicked (causing database inconsistencies)
2. Clear the cached guild pointer when the guild ID is cleared, upon error (dangling pointer).
3. Clear the (clientside) party name from all the party members when a party is disabanded (just visual).

Issues addressed: Point 2 is a possible cause of the crash described in #1266

[HerculesWSAPI]

This change is