Bugfix for numbering with ol sublists in themes BookMark & BookDark

Replaced :after with :before in the BookMark and BookDark themes because it seems to prevent this from happening:
![screenshot_ol-bug](https://cloud.githubusercontent.com/assets/9274322/4695129/1121791c-57e6-11e4-8296-3cddd8e48537.png)
I guess it has something to do with the CSS counter and how the reset of the sublist's ol affects it.