Fixes and some minor changes regarding teleports/portals code.

Gameplay changes:
hand-teleporter portals won't have a chance to fail anymore and you can teleport to an away mission.

Full stuff:
Made the teleporters (the one with the computer, power station and portal) link eachother at roundstart with initialize(). And also at New() because why not.
If you try to use the teleporter and the teleport was rejected for any reason (like having a nuclear disk), you won't get the chance to get a random damage from the teleport.
Fixes issue #2236.
Removed some spawn() calls.
Removed the chance of fail from the portal effects (the blue portals made with hand teleporters).
The portal datums will now return 0 if the teleport failed, and now use a new proc, start(), instead of New() to handle themselves.
Standarized teleport.dm from the helper_datums folder.
Removed the checks for centcomm z level and away missions z level for teleports. Now you can go there.
changed the /red messages from the teleports datum to span classes.
The "[something] bounces off of the portal!" were replaced for "The portal rejects [something]".
Removed an extra "the" on those messages.