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/ui/migration/MangaHolder.kt

@@ -9,8 +9,8 @@ import kotlinx.android.synthetic.main.source_list_item.thumbnail
 import kotlinx.android.synthetic.main.source_list_item.title
 
 class MangaHolder(
-    private val view: View,
-    private val adapter: FlexibleAdapter<*>
+    view: View,
+    adapter: FlexibleAdapter<*>
 ) : BaseFlexibleViewHolder(view, adapter) {
 
     fun bind(item: MangaItem) {

app/src/main/java/eu/kanade/tachiyomi/ui/migration/SelectionHeader.kt

@@ -25,7 +25,7 @@ class SelectionHeader : AbstractHeaderItem<SelectionHeader.Holder>() {
      * Creates a new view holder for this item.
      */
     override fun createViewHolder(view: View, adapter: FlexibleAdapter<IFlexible<RecyclerView.ViewHolder>>): Holder {
-        return SelectionHeader.Holder(view, adapter)
+        return Holder(view, adapter)
     }
 
     /**