Add ability to add aliases for names

[fiskenslakt]

Something like the /register command that lets you add arbitrary amounts of aliases associated with a name in the user table, which one can invoke instead of the name for pointing.

• Will require a new table (alias?) with a reference to the pzsd_user table.
• Adding logic to search through all the aliases if the initial name search during a point transaction fails to find a name
• New slash command(s) to add/remove/rename aliases (duh)

While the /register command is admin only, I think it's not unreasonable to make this command available to anyone, but I'm a little undecided on that.

[fiskenslakt]

Oh there should probably also be a command to list all current aliases for a given name as well.

[fiskenslakt]

As discussed in the server, we should drop the name column in the pzsd_user table and just have the new alias table be responsible for storing names associated with a user. There should be a column is_primary to denote what alias is the primary name, for purposes of displaying on leaderboards and such.