`roles`: Make it easier to type roles with complex names

[Arcensoth]

The way roles commands currently work is by using discord.py's RoleConverter under-the-hood. This is convenient for the implementation and for pingable roles that staff need to maintain, but it is not convenient for a user who's trying to join a role.

One solution is to allow arbitrary string input for these commands, and do a partial text match with role names.

Another solution is to implement aliases for roles, however this would require additional commands to manage the aliases.