Various smaller improvements

Improves Signs & Songs subtitle RegEx
Adds tests for the Signs & Songs subtitle RegEx
Automatically changes "enm" language to English
Makes the downscale converter select HEVC if the input is HEVC

src/main/java/net/knarcraft/ffmpegconverter/utility/SubtitleHelper.java

@@ -0,0 +1,30 @@
+package net.knarcraft.ffmpegconverter.utility;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * A helper class for subtitle-related tasks
+ */
+public final class SubtitleHelper {
+
+    private SubtitleHelper() {
+
+    }
+
+    /**
+     * Checks whether the given subtitle is a songs & signs subtitle
+     *
+     * @param subtitleTitle <p>The subtitle to check</p>
+     * @return <p>True if the subtitle is a songs and signs, not a full subtitle</p>
+     */
+    public static boolean isSongsSignsSubtitle(@NotNull String subtitleTitle) {
+        Pattern pattern = Pattern.compile("(^| |\\(|\\[\\{)si(ng|gn)s?($|[ &/+-@])+(titles)?[ &/+-@]?(songs?)?|" +
+                "(^| |\\(|\\[\\{)songs?($|[ &/+-@])+(si(gn|ng)s?)?|.*forced.*|.*s&s.*");
+        Matcher matcher = pattern.matcher(subtitleTitle.toLowerCase().trim());
+        return matcher.find();
+    }
+
+}