changes to overcome performance issues with huge fitnesse result files

(several MP)
![fitnesse_change_proposed](https://f.cloud.github.com/assets/6112131/1681526/0b283730-5d96-11e3-9691-8d84cdcf4ec0.png)

Hi,
our company had an issue with performance of this plugin due to huge fitnesse results. Since the fitnesse results are stored in build.xml this file had a size of several MB. Details are explained here: https://issues.jenkins-ci.org/browse/JENKINS-13936.

We overcome the issue as follows:
- do not store the fitnesse-results in build.xml, put them in separate files (in same directory as build.xml)
- in addition we added a new column to directly jump to the fitnesse history page

We would like to give back the changes if you are interested in. there is still some work to do 
- update test cases
- documentation

Please let me know if you are interested
Rico