fix permission checks on starboard interactions & manage_cogs

[andrewj-brown]

The default_permissions() decorator lets DMs through. This is cringe - we want to use default_permissions so that the server's role & moderation processes are abstracted out of the bot's code, and future committees can just fiddle with discord settings.

A more long-term solution is to have a decorator, @requires_server or the like, so we can continue to use default_permissions and just require that some commands must be used in the server. (This also would fix several other DM-based errors this PR identifies.) However, for now, let's just switch them all to checks.has_permissions() instead.

grep -r permission shows the following cogs use permissions:

• member_count: errors out on DMs anyway (should be fixed but who cares)
• minecraft: uses has_permissions() and Member-type-checks anyway
• remindme: has manual permission checks, these will throw AttributeError in DMs (should be fixed but who cares)
• starboard: fixed
• manage_cogs: fixed

[andrewj-brown]

Using mega gamer admin powers to merge instantly. it's a 3-line change, and I don't want people /manage_cogs unload'ing shit while this PR waits.

...also fuck typechecking