Externalize the dictionary pack's name and settings

Some changes downward the road need Latin IME to know the dictionary
pack by package name. This makes the name an external string.

Bug: 5095140
Change-Id: Ibebf5eb892af19681c18da38955e50dfb573330a
diff --git a/java/res/xml/prefs.xml b/java/res/xml/prefs.xml
index 552e3cf..2ff82f9 100644
--- a/java/res/xml/prefs.xml
+++ b/java/res/xml/prefs.xml
@@ -70,8 +70,8 @@
             android:title="@string/configure_dictionaries_title">
            <intent
               android:action="android.intent.action.MAIN"
-              android:targetPackage="com.google.android.inputmethod.latin.dictionarypack"
-              android:targetClass="com.google.android.inputmethod.latin.dictionarypack.DictionarySettingsActivity" />
+              android:targetPackage="@string/dictionary_pack_package_name"
+              android:targetClass="@string/dictionary_pack_settings_activity" />
         </PreferenceScreen>
         <ListPreference
             android:key="auto_correction_threshold"