New briefing layout

[BenLubar]

Goals for the new layout:

• Handle 8 marines plus some number of spectators without requiring scrolling
• Make room for longer item tooltips, allowing medals to display without the timed fade and to prepare for #508
• Need support for multiple teams (team deathmatch, and later #161)

There's a good layout on the workshop but we can't use it as the creator wants to keep creative control over it. We can, however, take inspiration from it and learn from what it does better than vanilla.

https://steamcommunity.com/sharedfiles/filedetails/?id=919279732

Required UI elements:

• Ready button (has a checkbox when not the lobby leader, changes label to Start Mission when lobby leader)
• Chat button (multiplayer only; not necessarily required, might be better to put a message about using the bind in instead)
• Voting button (takes you to player list panel; multiplayer only)
• Button to view leaderboard for current mission (multiplayer only)
• Change Mission button (singleplayer only)
• Invite Friends button (multiplayer only)
• Add Bot button
• Deselect Marines button
• Mission Details button (currently we have two of these but the non-text one is kinda unintuitive)
• Tooltip area (shows details about hovered marine, weapon, equipment, or medal; this needs to be bigger than it currently is to accommodate inventory item descriptions; gets replaced by vote when vote is active)
• Lobby leader
• Current difficulty settings
• Mission title
• Objectives summary

For each marine or player, we have a lobby row, which needs:

• Marine portrait
• Player avatar
• Player name (click for dropdown options)
• Marine class (for new players)
• Primary and secondary weapons (2:1 aspect ratio)
• Extra equipment (1:1 aspect ratio)
• Commander level
• Experience bar
• Promotion medal
• Medal equip slot
• Ready checkbox or leader crown
• Voice chat icon
• Possibly modify the row for players who are:
  • connecting
  • spectating
  • not the first marine per player (i.e. a bot)
  • the first local slot (the big one on the current layout)

The UI needs to work at 4:3, 16:9, and 16:10 aspect ratios, with at least 8 lobby rows visible without scrolling.

[Blueberryy]

Also please make separator (-) between difficulty and onslaught at the briefing info.

[BenLubar]

@jhh8 I'd recommend a translation string for %s1 Onslaught and one for Hardcore %s1 so languages can put separators in if they want