Add preference library and settings fragment placeholder

app/src/main/res/values/strings.xml

@@ -10,4 +10,6 @@
     <string name="menu_about">About</string>
     <string name="menu_github">GitHub</string>
     <string name="menu_credits">Credits</string>
+
+    <string name="placeholder">Placeholder</string>
 </resources>

app/src/main/res/xml/preference.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+    <PreferenceCategory android:title="@string/placeholder">
+        <EditTextPreference
+            android:key="username"
+            android:summary="@string/placeholder"
+            android:title="@string/placeholder" />
+        <EditTextPreference
+            android:key="password"
+            android:summary="@string/placeholder"
+            android:title="@string/placeholder" />
+    </PreferenceCategory>
+</PreferenceScreen>