Plugin retry fixes and refactoring

[SapiensAnatis]

• Closes Co-op retries should return to lobby when room is not full #244, a.k.a. Golden Experience Requiem bug by returning players to the lobby when retrying after at least one player has given up.
• Retries when failing a quest are still a bit glitchy -- it's supposed to remove players who voted no and allow players who voted yes to optionally rejoin the room similar to the prompt on a successful clear. Currently any retry where all players are dead will go back to the lobby. Failed retry votes on quest failure should prompt players to rejoin quests #378 raised to track.

Plugin refactoring:

• Remove HeroParam and other custom actor properties and persist this state in the plugin class, since only the plugin needs to know about these. It's tidier and avoids Photon having to serialize them (and crashing in the case of HeroParam since we didn't register this type).
• Use enums for event codes.
• Improve logging and add info logs which can provide basic diagnostics, particularly around potential problem areas such as GoToIngameState