Makes it possible to enable debug mode

Debug mode is now enabled if the property `debug = true` is set in `conf/config.properties`
Changes code for reading internal configurations
Changes many primitive lists to List<>
Adds some missing annotations
Renames the main class

src/main/java/net/knarcraft/ffmpegconverter/converter/Converter.java

@@ -3,9 +3,11 @@ package net.knarcraft.ffmpegconverter.converter;
 import net.knarcraft.ffmpegconverter.container.FFMpegCommand;
 import net.knarcraft.ffmpegconverter.container.StreamProbeResult;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.io.File;
 import java.io.IOException;
+import java.util.List;
 
 /**
  * This interface describes a file converter
@@ -18,7 +20,7 @@ public interface Converter {
      * @return <p>A list of valid input formats</p>
      */
     @NotNull
-    String[] getValidFormats();
+    List<String> getValidFormats();
 
     /**
      * Converts the given file
@@ -36,6 +38,7 @@ public interface Converter {
      * @param outFile     <p>The output file</p>
      * @return <p>A list of commands</p>
      */
+    @Nullable
     FFMpegCommand generateConversionCommand(@NotNull String executable, @NotNull StreamProbeResult probeResult,
                                             @NotNull String outFile);