Minor Change to PocketManager

Added a minor check to PocketManager.loadDimension() so that an attempt
to load an unregistered dimension won't be passed on to Forge where it
would cause an exception - which is then caught by Forge before it can
cause problems. This isn't strictly necessary, but it's a nice
consideration.
Removed CommandDeleteAllLinks

I removed CommandDeleteAllLinks because of the significant risk that it
would harm a server. It's possible that someone could run this by
accident instead of CommandDeleteRifts. It takes the same arguments or
even no arguments and it would immediately wipe all links in a
dimension. We can restore it later if it's really needed.
Minor Change

Removed a reference to CommandDeleteAllLinks from mod_pocketDim.
Rewrote CommandTeleportPlayer

Rewrote CommandTeleportPlayer for the same reason as usual. There were a
few bugs before, such as that lookups for players were limited to within
the world from which the command sender was using the command. Players
in other dimensions could not be teleported. The command would also
place people in the ground because it did not adjust its coordinates for
the way that DDTeleporter interprets them - as the location of the top
block of a door and the player's head.