fixed some portal and teleportation issues

CmdExecutor.java:
  - buildPortalFrame:
    - now takes the orientation of the portal as parameter
    - now builds the portal based on the orientation
    - improved the removing of blocks around the portal

NetherPortListener.java:
  - onPlayerPortalEnter:
    - added determination of portal orientation, based on player
orientation

  - onPortalCreate:
    - added determination of portal orientation, based on specific
block formations

  - new function 'safeTeleport' for getting a better position for
teleport (attempt to fix that sometimes players will be teleportet
above the portal)