Restructure files & remove unused code & simplify few statements

src/main/java/at/pcgamingfreaks/mkvaudiosubtitlechanger/model/MkvToolNix.java

@@ -0,0 +1,17 @@
+package at.pcgamingfreaks.mkvaudiosubtitlechanger.model;
+
+public enum MkvToolNix {
+    MKV_MERGER("mkvmerge.exe"),
+    MKV_PROP_EDIT("mkvpropedit.exe");
+
+    private final String file;
+
+    MkvToolNix(String file) {
+        this.file = file;
+    }
+
+    @Override
+    public String toString() {
+        return file;
+    }
+}