Fixed text case issue which causing problem in some languages

![](http://i.imgur.com/qpMf6pc.png)

When using `ToLower()` in Turkish `I` becomes `ı` and therefore app unable to find filename because expected char was `i`. To solve this problem need to use invariant culture when doing text comparison or case changes.

![](http://i.imgur.com/dhiWKTl.png)

Also UI have this problem too but i can't find where this case change happens, probably because it is inside `MahApps.Metro.dll`?