Add gamerules implementation

This PR adds default vanilla game rules for the /gamerule command.

I've linked the "doDaylightCycle" option to the world time.

Note: currently, GlowKit gamerule command implementation is blocking the user to add custom gamerules. I found it weird and I'd like to have your point of view: do we really want to restrict it ?

Related issue/PR:
 - #455