Several Updates for l10n

Last Pull request (https://github.com/klangfarbe/Go-for-WordPress/commit/beef7d25d3eaffe8b344efac5454e6feaf579e05) was broken. My bad, I'm not perfectly used to Git.... 

Here a complete one with all changes:

### l10n
* Added possibility to translate Backend
* Added german translation
* Updated Plugin-Header to make it translateable.

### WGo
* Added French WGo-Translation to Options-Menu
* Updated Chinese and Czech WGo-Translation