feat(content): slayer skill

[hex-agon]

Some initial scripts related to the slayer skill, for whenever we get there...

Demo: https://streamable.com/9djx45

Things that are done:

• Slayer tasks up to around june 2006
• Slayer introduction chat
• Generic slayer master chat
• Slayer gem chat

There are still things that need to be done:

• The slayer skill does not exist, it currently gives runecraft exp
• The slayer master shop
• The current slayer task 'table' is just a placeholder and there's only one
• The task extra checks are placeholders as the quest varp/varbits do not exist yet
• Npc/Obj types
• Slayer npcs combat scripts
• Slayer npcs spawns

This PR only works if you're running the server with BUILD_VERIFY=false as it's technically adding 'custom' content

[FlenarnTemp]

This looks great, but I'm not 100% sure on if this is something we would necessarily ever merge in this repository. As of right now, it'll most likely be another half year, if not more, before we even leave the 225 revision, and another good chunk of time before we're at January 2005 when Slayer is introduced.

This might be more suitable to close, and re-open when the time comes with focus being on content we have in the current revision, even more so as it's a bit unclear how the Github structure will be once we consider 225 complete.