Added uncuff signs.

These are signs which will uncuff all the players you have cuffed at the time.
Additionally (optional), commands ( uncuff-sign-commands in config) may be run by the cuffing player when the sign is clicked. These commands have the {cuffed} placeholder for the cuffed player.
If multiple players were cuffed, then the commands will be executed for each cuffed player.

One can set an uncuff sign using the /setuncuffsign command ( cuffem.setuncuffsign permission node, defaults to OP).
The data for this sign is saved within the sign. So removing/breaking the sign will remove this data.


Improvements to commands

Some internal changes and slight improvements to tab-completion.

You are now unable to uncuff players that were cuffed by somebody else (previously possible) unless you have the cuffem.uncuff.other permission node (defaults to OP).