Some templates work

This PR separates some common template elements (I realised later that some are probably useless... :disappointed: ) and reuse them around when necessary (mainly the poster area in Display and Pm and the list of boards (in BoardIndex and MessageIndex).

@Spuds that's what I was referring to [here](http://www.elkarte.net/index.php?topic=494.msg5232#msg5232) :angel: