Fix flags getting erroneously hidden or optional

[davidliu]

The optional/hidden functions modify the original flag passed in rather than create their own copy. This ends up displaying the wrong options in the help menu for a command. For example, lk room send-data requires the --room flag, but running help on the command gives this:

NAME:
   lk room send-data - Send arbitrary JSON data to client

USAGE:
   lk room send-data [OPTIONS] DATA

OPTIONS:
   --topic TOPIC                          TOPIC of the message
   --identity value [ --identity value ]  One or more participant identities to send the message to. When empty, broadcasts to the entire room
   --help, -h                             show help (default: false)

It also allows running the command itself, not raising that the room flag wasn't set.

[rektdeckard]

Thanks for spotting!