JDK8, lint fixing (#2888)

* Use Kotlin JDK8

* Satisfy a ton of lints

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

app/src/test/java/eu/kanade/tachiyomi/data/backup/BackupTest.kt

@@ -40,7 +40,7 @@ import uy.kohesive.injekt.api.addSingleton
  * Test class for the [BackupManager].
  * Note that this does not include the backup create/restore services.
  */
-@Config(constants = BuildConfig::class, sdk = intArrayOf(Build.VERSION_CODES.LOLLIPOP))
+@Config(constants = BuildConfig::class, sdk = [Build.VERSION_CODES.LOLLIPOP])
 @RunWith(CustomRobolectricGradleTestRunner::class)
 class BackupTest {
     // Create root object

app/src/test/java/eu/kanade/tachiyomi/data/database/CategoryTest.kt

@@ -72,7 +72,7 @@ class CategoryTest {
 
         // It should not have 0 as id
         val c = db.getCategories().executeAsBlocking()[0]
-        assertThat(c.id).isNotZero()
+        assertThat(c.id).isNotZero
 
         // Add a manga to a category
         val m = db.getMangas().executeAsBlocking()[0]