Extract Input Settings preference header string.

Fixes #1159

FREEBIE

res/values/strings.xml

@@ -649,6 +649,7 @@
     <string name="preferences__pref_all_mms_title">Receive all MMS</string>
     <string name="preferences__use_textsecure_for_viewing_and_storing_all_incoming_text_messages">Use TextSecure for viewing and storing all incoming text messages</string>
     <string name="preferences__use_textsecure_for_viewing_and_storing_all_incoming_multimedia_messages">Use TextSecure for viewing and storing all incoming multimedia messages</string>
+    <string name="preferences__input_settings">Input Settings</string>
     <string name="preferences__enable_enter_key_title">Enable Enter key</string>
     <string name="preferences__replace_smiley_with_enter_key">Replace the smiley key with an enter key</string>
     <string name="preferences__pref_enter_sends_title">Enter sends</string>

res/xml/preferences.xml

@@ -72,7 +72,7 @@
 
   </PreferenceCategory>
 
-  <PreferenceCategory android:title="Input Settings">
+  <PreferenceCategory android:title="@string/preferences__input_settings">
       <CheckBoxPreference android:defaultValue="false"
                           android:key="pref_enter_key"
                           android:title="@string/preferences__enable_enter_key_title"