Fix issue-953: gave the annotation category pane a percentage-based width and added a min-width to the body.

![Screen shot 2013-01-20 at 11 43 42 PM](https://f.cloud.github.com/assets/817212/82262/160ea92a-6398-11e2-966e-7c32525c0313.png)

In reference to https://github.com/MarkUsProject/Markus/issues/953
The min-width added to the body is less than that which already exists for the header, so I'm not imposing any restrictions not previously done.