[ThemePicker] Add bottom navbar to main activity

Set up the basic layout and add a bottom nav bar to
CustomizationPickerActivity, with basic support for
switching between section fragments.
(Fragments to be added in a separate CL)

Bug: 120560581
Change-Id: I06832260d20ca2938b6c04e110fadf45bc3070a2
diff --git a/res/menu/bottom_navigation_menu.xml b/res/menu/bottom_navigation_menu.xml
new file mode 100644
index 0000000..4954206
--- /dev/null
+++ b/res/menu/bottom_navigation_menu.xml
@@ -0,0 +1,35 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+     Copyright (C) 2018 The Android Open Source Project
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+<menu xmlns:android="http://schemas.android.com/apk/res/android">
+    <!-- TODO (santie): replace icons with real ones when available -->
+    <item
+        android:id="@+id/nav_theme"
+        android:title="@string/theme_title"
+        android:icon="@drawable/ic_nav_theme" />
+    <item
+        android:id="@+id/nav_clock"
+        android:title="@string/clock_title"
+        android:icon="@drawable/ic_nav_theme" />
+    <item
+        android:id="@+id/nav_grid"
+        android:title="@string/grid_title"
+        android:icon="@drawable/ic_nav_theme" />
+    <item
+        android:id="@+id/nav_wallpaper"
+        android:title="@string/wallpaper_title"
+        android:icon="@drawable/ic_nav_theme" />
+</menu>
\ No newline at end of file