v5: Add Corporation Wardec notifications

[moppa]

V5 re-implementation of #91

• Adds notification for the WarDeclared notification which is sent to Corporations when a war declaration is made.
• Fixes an issue that the notification fails if the attacker or defender does not exist in UniverseName yet.

If the UniverseName is not yet populated then the category property is null. Which makes the call to zKillBoardToDiscordLink fail with the error

zKillBoardToDiscordLink(): Argument #1 ($type) must be of type string, null given