Slight update to portals

[Yukar9]

I've made some updates to the portals. Firstly, they can now be placed in either direction. Secondly, they are now created by placing a diamond block and lapis block inside of them, so the /portal buy and /portal set commands are no longer used.

There were 2 players who had deposited diamonds and lapis for portals, they will have their deposits refunded.

The portals already built/being built have not been affected.

Please see the wiki page for updated information on how to use portals.

[A. Pippenger]

This is a big improvement, thanks for taking the time to do it.