Added CyclerGadget - generic enum cycler
Eliminates a lot of redundant code around cycling through enum values and adds a more consistent look & feel to enum cycler buttons.

Also added "stb.access.modify" permission; allows players to change the access control settings of blocks they don't own.
Added RESTRICTED access mode
Only owner and owner's friends can use blocks in restricted mode.
Added /stb friend and /stb unfriend commands to manage friends.