Sole Survivor/additional mod support

This is a bucket list of items that will be required to support a Sole Survivor game mode. Some features might not be attainable (such as joining a game in-progress) and I may have missed a few, so this is high-level but covers a fair bit of it.

• Live game joining (depends on Save/Load serialization of game state)
• Support SS map format through utility import (works in another branch, requires PR)
• Add entries for SS assets to the global mix database (not required, but useful)
• Always show unit health bars (via #4054)
• Spawning varying types of crates (via #4360)
• Allow for individual stat leveling of hero units - armor, damage, movement speed, rate of fire, weapon range - seen here. This will take some thought because the current experience points system levels up all of these stats equally (via #4383).
• Introduce new modifiers for rate of fire (via #6079)
• Introduce new modifiers for weapon range (it's done but not sure when)
• Crates to level up individual stats. (via #4383)
• Art for new crates - potentially use SS' existing crates, but these need to have shadows added to them, and potentially also effects for floating in water (RA mod support). Potentially use the wooden crate, and do a ton of palette remaps to them for varying colors.
• New art / interface similar to sole survivor, as a start. Work in progress seen here: original game image, 1st attempt, 2nd attempt (improvement)
• Logic for specifying custom UI in a map.yaml/map.lua
• Always showing the player's name above a player's "hero" unit (via #4393).
• Capture the Flag logic, or other objective based game logic (e.g. deathmatch).
• Allow an option to choose which announcer pack to use
• Attaching EVA announcer clips to specific events (a certain type of crate was picked up, or an objective was met).
• Custom crate behavior mentioned here: http://www.cnc-source.com/?page=content/ss/ssmisc
• Tooltip changes - only show the unit name on the tooltip, hide country + name. This is currently done for neutral actors, but there should be a flag that can be set in the yaml. #6613

This is a broad checklist rather than a single scoped change, with references to map.yaml/map.lua, the utility import, and the global mix database. Start by selecting one unchecked item and locating its existing entry point; define the affected behavior and tests or in-game checks that demonstrate it is complete before beginning work.