Generate @command usage messages from the invoked command name

[MrKeiKun]

Pull Request Prelude

• I have followed proper Hercules code styling.
• I have read and understood the contribution guidelines before making this PR.
• I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

Command usage messages hardcoded their command names and alias lists, so they
drifted out of sync with conf/atcommand.conf and could not reflect a server's
actual configuration.

This replaces the hardcoded names with a %s filled from the command the player
actually typed, as suggested by @MishimaHaruna in the issue:

The easiest fix would probably be to show the version of the command that was
issued (If you are using the 'ban' command, there's no need for it to also
display 'banish'), and the help strings could simply contain a %s token where
the command name should be displayed.

Before:

@baselvlup            ->  Please enter a level adjustment (usage: @lvup/@blevel/@baselvlup <number of levels>).

After:

@baselvlup            ->  Please enter a level adjustment (usage: @baselvlup <number of levels>).
@blvl                 ->  Please enter a level adjustment (usage: @blvl <number of levels>).
#blvl <charname>      ->  Please enter a level adjustment (usage: #blvl <number of levels>).

This also fixes messages that named the wrong command entirely: @blvl, @jlvl
and @glvl listed only aliases and never their own name; @shownpc reported
usage: @enablenpc, which does not exist; and @nuke, @partyspy and
@guildspy reported the usage of the command they shared a message with.

Note that translations will need the same %s change. The surrounding text is
untouched, so only the usage portion is affected.

Issues addressed: #228