Update jquery.tablesorter.js to 2.17.8

This should fix issue #441 

Removes also sorting on the last column ('Action').
![screen shot 2014-09-29 at 00 33 22](https://cloud.githubusercontent.com/assets/1818657/4435965/a4c9bf40-475f-11e4-9a1b-b282d56ab987.png)