Replace changelog dialog with controller, move migration logic to a separate class

app/src/main/java/eu/kanade/tachiyomi/Migrations.kt

@@ -0,0 +1,53 @@
+package eu.kanade.tachiyomi
+
+import eu.kanade.tachiyomi.data.library.LibraryUpdateJob
+import eu.kanade.tachiyomi.data.preference.PreferencesHelper
+import eu.kanade.tachiyomi.data.preference.getOrDefault
+import eu.kanade.tachiyomi.data.updater.UpdateCheckerJob
+import java.io.File
+
+object Migrations {
+
+    /**
+     * Performs a migration when the application is updated.
+     *
+     * @param preferences Preferences of the application.
+     * @return true if a migration is performed, false otherwise.
+     */
+    fun upgrade(preferences: PreferencesHelper): Boolean {
+        val context = preferences.context
+        val oldVersion = preferences.lastVersionCode().getOrDefault()
+        if (oldVersion < BuildConfig.VERSION_CODE) {
+            preferences.lastVersionCode().set(BuildConfig.VERSION_CODE)
+
+            if (oldVersion == 0) return false
+
+            if (oldVersion < 14) {
+                // Restore jobs after upgrading to evernote's job scheduler.
+                if (BuildConfig.INCLUDE_UPDATER && preferences.automaticUpdates()) {
+                    UpdateCheckerJob.setupTask()
+                }
+                LibraryUpdateJob.setupTask()
+            }
+            if (oldVersion < 15) {
+                // Delete internal chapter cache dir.
+                File(context.cacheDir, "chapter_disk_cache").deleteRecursively()
+            }
+            if (oldVersion < 19) {
+                // Move covers to external files dir.
+                val oldDir = File(context.externalCacheDir, "cover_disk_cache")
+                if (oldDir.exists()) {
+                    val destDir = context.getExternalFilesDir("covers")
+                    if (destDir != null) {
+                        oldDir.listFiles().forEach {
+                            it.renameTo(File(destDir, it.name))
+                        }
+                    }
+                }
+            }
+            return true
+        }
+        return false
+    }
+
+}