Added Slovenian translation

Hi,

I've translated the texts on CrowdIn -- here's a pull request for your convenience. I've compiled the app and tested it in Slovenian as much as I could (sending/receiving, bakcup/verify, Local Trader). I think the translation is ready. I've also run it through a spell checker.

I don't know what to do with MessageBundle_xx.properties though (but I imagine it's a server-side resource file).

I use Mycelium as my day-to-day wallet so I'll keep improving the translations when they are live.