Issue 435 issues category

Ref: https://github.com/OpenUserJs/OpenUserJS.org/issues/435
After: https://github.com/OpenUserJs/OpenUserJS.org/pull/443
Fixes: https://github.com/OpenUserJs/OpenUserJS.org/issues/199

* Added new category "_Issues_" in forum;
    * Listing contains only discussions with category `issues`.
    * Sub-forum is accessible from [http://localhost:8080/issues](http://localhost:8080/issues) and [http://localhost:8080/forum/issues](http://localhost:8080/forum/issues) per existing route logic.
    * 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.
* Added new category "_All Discussions_" in forum;
    * Listing contains all discussions (including category `issues`).
    * Sub-forum is accessible from [http://localhost:8080/all](http://localhost:8080/all) and [http://localhost:8080/forum/all](http://localhost:8080/forum/all) per existing route logic.
    * Description is "Overview of all discussions" (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.
* Moved unknown (e.g. `all` and `issue`) category logic to modelParser.
* Fixed trailing `,` on last item in object list.

![Main forum](https://cloud.githubusercontent.com/assets/55841/5172897/20e517d2-7424-11e4-95a5-420535f17179.jpg)

![Sub-forum Issues](https://cloud.githubusercontent.com/assets/55841/5159709/c7ebbe56-736f-11e4-844f-055e22b468ae.jpg)

**Updated**