Add optional to automatically download new chapers (#538)

* Add optional to automatically download new chapers

* Only trigger download once

app/src/main/java/eu/kanade/tachiyomi/data/preference/PreferenceKeys.kt

@@ -89,6 +89,8 @@ class PreferenceKeys(context: Context) {
 
     val startScreen = context.getString(R.string.pref_start_screen_key)
 
+    val downloadNew = context.getString(R.string.pref_download_new_key)
+
     fun sourceUsername(sourceId: Int) = "pref_source_username_$sourceId"
 
     fun sourcePassword(sourceId: Int) = "pref_source_password_$sourceId"

app/src/main/java/eu/kanade/tachiyomi/data/preference/PreferencesHelper.kt

@@ -134,4 +134,6 @@ class PreferencesHelper(context: Context) {
 
     fun hiddenCatalogues() = rxPrefs.getStringSet("hidden_catalogues", emptySet())
 
+    fun downloadNew() = prefs.getBoolean(keys.downloadNew, false)
+
 }