Pools ext tweaks/additions.

Made a few small tweaks and additions to the pools ext.

* Changed the pool title to be unique (with a UNIQUE index).
* Fixed up the error reporting to use the BaseThemelet function rather than it's own as mentioned in commit 09a18b87102824aa04111ca040505d5e3eda9eed.
* Pool navigation box should now show on pool/view pages.
* Added an "Order By" box which allows sorting the pool list by various methods (Recently created, Last updated, Name & Post count).
* Added a box on the pool edit page to allow modifying the pool description. Seemed a bit odd that this wasn't here to begin with..
* Added the ability to set pool / source via tag. "source:URL" for source, and "pool:ID/TITLE" for pool.