Task overview: Hide client prefix in issuer value for a one client setup...

In a one client setup the prefixed client title is not necessary:
![bildschirmfoto 2014-04-11 um 12 40 34](https://cloud.githubusercontent.com/assets/485755/2679270/1b2a945a-c170-11e3-8bbc-6f5f189dc7ea.png)

Additionaly i add tests for the different possabilities for the issuer display.

@lukasgraf 

(this pr replace #234)