Remove last String stuff, to make plugin work in QGIS 2.x

Hi Olivier,
I've tested the plugin on 2.2 and had to fix some other things. Please have a look at this.

2 issues remain open, 

- sometimes the QgsProject is None. I've asked on the mailinglist. But another solution would be to add the IF as you did, but then ask the user to use saveAs, or just warn him that saving had a problem? It works most of the times with me though...
- I had another issue with self.factor, which seemed None. But I can not reproduce this.

For me it is ok, to just release this version and keep it experimental. Then later invest some time to do the clean version.

Regards,

Richard Duivenvoorde