Label Kitsu login field as email address instead of username

app/src/main/res/layout/pref_account_login.xml

@@ -23,6 +23,7 @@
         android:background="@color/dividerLight" />
 
     <TextView
+        android:id="@+id/username_label"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:text="@string/username" />

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

@@ -341,6 +341,7 @@
     <!-- Login dialog -->
     <string name="login_title">Log in to %1$s</string>
     <string name="username">Username</string>
+    <string name="email">Email address</string>
     <string name="password">Password</string>
     <string name="show_password">Show password</string>
     <string name="login">Login</string>