Rewrote UpdateDownloader to Kotlin

Added auto update check (every 12 hour)
Warning message optional fix #256
Lots of bug fixes!

app/src/test/java/eu/kanade/tachiyomi/data/library/LibraryUpdateAlarmTest.java

@@ -101,7 +101,7 @@ public class LibraryUpdateAlarmTest {
     @Test
     public void testLibraryUpdateServiceIsStartedWhenUpdateIntentIsReceived() {
         Intent intent = new Intent(context, LibraryUpdateService.class);
-        intent.putExtra("is_forced", false);
+        intent.putExtra("is_manual", false);
         assertThat(app.getNextStartedService()).isNotEqualTo(intent);
 
         LibraryUpdateAlarm alarm = new LibraryUpdateAlarm();