Multiple roles, forced role sync and linked Roblox accounts

• Several roles per staff member. Someone can now be a Moderator and a Developer at once, and their permissions combine. /whitelist adds a role, and /unwhitelist removes one role or all of them.
• Forced role sync. Turn it on and RoWarden reverts manual role changes made directly in Discord or in your Roblox group, so the dashboard stays the single source of truth.
• Multiple Roblox accounts. Link up to five Roblox accounts to one RoWarden account and give each its own roles. Useful for staff with a separate testing or alt account.

I also fixed role checkboxes not syncing correctly in some cases.