Add defunct modding usergroups & pubble stubs

[JBHyperion]

Part of #3163 - Adds stub wiki articles for the MAT, BAT, MAT Leaders, BAT Managers and the proto-bubble icon

Looking for help with history of the BAT stub article in particular

[cl8n]

some formatting things to keep in mind

• metadata has to be surrounded by --- to do anything, for example

  ---
  tags:
    - MAT
  ---
  
  # Mapping Assistance Team

• titles don't need linguistic articles("the"/"a"/"an") at the start, so here The Beatmap Appreciation Team should be Beatmap Appreciation Team
• sections don't need to be qualified by the title again, here History of the BAT should be History
• an article not clearly missing any info for what it's trying to be isn't a stub
• first mentions of acronyms or alternate names should be italicised to show that you may refer to them again like that
• should probably refer to acronyms in further usages instead of the full name (repeating something like "Quality Assurance Team" five times gets tiring to read)

[JBHyperion]

@cl8n Cleaned up everything from your review regarding style and metadata tagging. Regarding

an article not clearly missing any info for what it's trying to be isn't a stub

I can't guarantee these articles aren't missing information, since everything written here took place before I started modding and I can only go based on old hearsay and buried forum posts. If someone with better knowledge can confirm they contain everything they need to contain, then the stub tag can be removed.

[peppy]

pubble lives on!

[MegaApplePi]

Suggested change

	These positions were later held by [Charles445](https://osu.ppy.sh/users/85000), [Loctav](https://osu.ppy.sh/users/71366) and [popner](https://osu.ppy.sh/users/759860) from the 22nd of December 2013 until the separation of the BAT into the Beatmap Nomination Group (later the [Beatmap Nominators](/wiki/People/The_Team/Beatmap_Nominators)) and the Quality Assurance Team on the 21st of August, 2014.
	These positions were later held by [Charles445](https://osu.ppy.sh/users/85000), [Loctav](https://osu.ppy.sh/users/71366), and [popner](https://osu.ppy.sh/users/759860) on the 22nd of December 2013, until the BAT was separated into the Beatmap Nomination Group (later the [Beatmap Nominators](/wiki/People/The_Team/Beatmap_Nominators)) and the Quality Assurance Team on the 21st of August, 2014.

[MegaApplePi]

Suggested change

	These positions were later held by [Charles445](https://osu.ppy.sh/users/85000), [Loctav](https://osu.ppy.sh/users/71366) and [popner](https://osu.ppy.sh/users/759860) from the 22nd of December 2013 until the separation of the BAT into the Beatmap Nomination Group (later the [Beatmap Nominators](/wiki/People/The_Team/Beatmap_Nominators)) and the Quality Assurance Team on the 21st of August, 2014.
	These positions were later held by [Charles445](https://osu.ppy.sh/users/85000), [Loctav](https://osu.ppy.sh/users/71366), and [popner](https://osu.ppy.sh/users/759860) on the 22nd of December 2013.
	On the 21st of August, 2014, the BAT was separated into the Beatmap Nomination Group (later the [Beatmap Nominators](/wiki/People/The_Team/Beatmap_Nominators)) and the Quality Assurance Team.

I was thinking that this sentence was long, maybe it could be split up into two?