Permissions are duplicated across database and code

https://github.com/CUCB/website/blob/02732fdb29181fad501d89b426029e3fe2c672ca/src/seeders/DatabaseSeeder.ts#L17-L201 contains a load of definitions for permissions and should have enough information to determine which users can do what, but in https://github.com/CUCB/website/blob/02732fdb29181fad501d89b426029e3fe2c672ca/src/lib/permissions.ts#L4-L46 we don't touch this. We should show a summary of what permissions people have and what those mean.

This stuff should be defined once. It doesn't really matter whether that is a code thing or a database thing, but it should be defined once.