nickserv: Improve detection of forced nicks vs normal nicks
nickserv: Update default nick_timeout to 30
nickserv: Improve behaviour when the impossible happens
nickserv: After adding a nick, check if another user is already on that nick

This clears up a bug where a user that held a registered nick since before it was registered
could continue to hold it.
This bug doesn't occur in 0.2 as there was no way to register a nick without being the current holder.
nickserv: Prevent messages from nicks which are still being checked

NOTE: The 0.2 services stopped all but a small whitelist of commands.
Here we ONLY stop PRIVMSG. This is mainly because I couldn't figure out how to trigger an action
for commandpermission for ALL commands, as opposed to specific ones.
nickserv: Add full-stops to error messages
nickserv: Misc style fixes
nickserv: Add some more command aliases
nickserv: Improve command permissions to cover all commands