Spawnweapons rework

[OttoRocket-LVP]

A todo list of things to be done to improve QoL around (persistent) spawnweapons.

• [x] Make it possible to use /my from the JavaScript code.
• [x] Make it possible to buy standard spawnweapons.
• • [ ] (Reminder: Make a list of buyable weapons)
• [ ] Make some fancy menu if one only uses /my spawnweapons to buy from there. *
• [ ] Make it possible to unlock and buy persistent weapon slots from achievements.
• • [ ] Make it possible to buy weapons with limited ammo for those weapon slots.

[EPIC-striker]

Can we give them access to the /weapons command?