Updated pit kiln rendering

Updated pit kiln rendering and made pit kilns require solid sides or they will eject.

![2014-12-10_23 29 19](https://cloud.githubusercontent.com/assets/5393249/5423461/be0c8f90-82b6-11e4-9153-5084a66de791.png)

![2014-12-10_23 35 57](https://cloud.githubusercontent.com/assets/5393249/5423463/cb457faa-82b6-11e4-86c2-39135a6e1d06.png)

![2014-12-10_23 39 53](https://cloud.githubusercontent.com/assets/5393249/5423467/df526292-82b6-11e4-926d-9e73bfac369a.png)

Moved all pottery tile entity rendering to the TESR as it was being rendered in two places and the simple block renderer wasn't sufficient for the end result.

The pit kiln now requires solid sides, when I started this I was able to make free standing pit kilns, light them and get finished pottery when they completed.

There is an outstanding issue with falling blocks, this is the same issue as was discovered in #702 but hasn't been fixed in this update because the issue isn't actually a problem with pottery (or the log piles) themselves. The same issue happens with any block that isn't considered a normal block but has a solid top surface (chiselled stone is another example). I have left the implemented fix on the log piles because they require a cover or you can't make charcoal but this will probably need a generalised fix so I will raise it as an issue.