Fix admin/committee ping permissions, fix timezone issues

[LimaoC]

This should fix an issue with members not being recognised as administrators (also it now checks for the "Committee" role rather than administrator perms). The datetime/timezone issues should hopefully also be fixed now too.

[andrewj-brown]

As far as perms go, and this is purely personal preference, I'd like bot stuff to be based off actual specific permissions, not role names - i.e. the starboard perm checks aren't "do you have the committee role", they're "do you have Manage Server / Manage Messages". I'd suggest tying this to the "Mention @\everyone" permission, rather than searching for a named committee role.

[LimaoC]

Making the perms role-based was an arbitrary choice so I'm happy to change them to be based on guild permissions.

• Bypassing reminder limit will require manage_guild permissions
• Mentioning other users/roles in reminders will require mention_everyone permissions

AFAIK manage_guild permissions are given to the infra role as well, but I do think there are cases where having commands be committee-only are necessary (e.g. drawing advent of code winners). I suppose in that case we can tie those commands to some other permission that's only given to committee.

[andrewj-brown]

Making the perms role-based was an arbitrary choice so I'm happy to change them to be based on guild permissions.

* Bypassing reminder limit will require `manage_guild` permissions

* Mentioning other users/roles in reminders will require `mention_everyone` permissions

AFAIK manage_guild permissions are given to the infra role as well, but I do think there are cases where having commands be committee-only are necessary (e.g. drawing advent of code winners). I suppose in that case we can tie those commands to some other permission that's only given to committee.

Yep, manage_guild is the only perm that Infra currently has over @\everyone (IIRC, I can't actually check, on account of "don't have manage_roles to confirm").

The breakdown of bot perms (pre-this-PR) is:

• manage_guild used for /starboard_cleanup, /membercount force=True, /mcwhitelist, /mcadmin: because it's the only perm Infra have, and those commands are either "bot's fucked" or they're just a convenience that we could mimic by connecting to the MC server directly anyway
• manage_messages used for starboard blacklist/unblacklist: because deleting messages

As far as a generic, committee-but-not-infra perm goes (to use for the reminder limit in this PR, or drawing AoC winners), I'd suggest manage_events.

[LimaoC]

Sounds good to me