Issue 435 issues category

Ref: https://github.com/OpenUserJs/OpenUserJS.org/issues/435
After: https://github.com/OpenUserJs/OpenUserJS.org/pull/443

* Added new category 'Issues' in forum;
    * Sub-forum is accessible from [http://localhost:8080/issues](http://localhost:8080/issues).
    * Description is 'Discussions on scripts' (I'm open to a different/better description when really needed).
    * One can not post a new discussion/issue from within the sub-forum (button is disabled).
    * Category column is back in this sub-forum, for linking to script's issues page.
* Removed all discussions with category issue from main forum.

![Main forum](https://cloud.githubusercontent.com/assets/55841/5159708/c539dbb6-736f-11e4-949b-c88d3d1df674.jpg)
![Sub-forum Issues](https://cloud.githubusercontent.com/assets/55841/5159709/c7ebbe56-736f-11e4-844f-055e22b468ae.jpg)

Yeah, was thinking about that, I just copied it from `categoryListPage`. Will do when I get home.