Better looking mkvtoolnix icons.

These two new icons are for the mkvinfo and mkvmerge GUI programms.
![mkvinfo](https://cloud.githubusercontent.com/assets/239049/5048100/5ca03cae-6c1b-11e4-8b18-6ef9c131bb1c.png) ![mkvmergegui](https://cloud.githubusercontent.com/assets/239049/5048101/5ca9b8d8-6c1b-11e4-9d53-1b60a695a6fa.png)