JDK8, lint fixing (#2888)

* Use Kotlin JDK8

* Satisfy a ton of lints

* Run res/layout files (and manifest) through reformatter

app/src/main/java/eu/kanade/tachiyomi/data/download/DownloadCache.kt

@@ -259,7 +259,7 @@ class DownloadCache(
      */
     private inline fun <K, V, R> Map<out K, V>.mapNotNullKeys(transform: (Map.Entry<K?, V>) -> R?): Map<R, V> {
         val destination = LinkedHashMap<R, V>()
-        forEach { element -> transform(element)?.let { destination.put(it, element.value) } }
+        forEach { element -> transform(element)?.let { destination[it] = element.value } }
         return destination
     }
 

app/src/main/java/eu/kanade/tachiyomi/data/download/DownloadService.kt

@@ -106,7 +106,7 @@ class DownloadService : Service() {
      * Not used.
      */
     override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
-        return Service.START_NOT_STICKY
+        return START_NOT_STICKY
     }
 
     /**

app/src/main/java/eu/kanade/tachiyomi/data/download/Downloader.kt

@@ -283,7 +283,7 @@ class Downloader(
                 // Do when page is downloaded.
                 .doOnNext { notifier.onProgressChange(download) }
                 .toList()
-                .map { _ -> download }
+                .map { download }
                 // Do after download completes
                 .doOnNext { ensureSuccessfulDownload(download, mangaDir, tmpDir, chapterDirname) }
                 // If the page list threw, it will resume here