Revert "Replace image with gradient color"

This reverts commit b0412b4f1f.

src/main/res/drawable/background_header.xml

@@ -1,11 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<shape xmlns:android="http://schemas.android.com/apk/res/android"
-    android:shape="rectangle" >
-    <gradient
-        android:centerColor="@color/material_primary_300"
-        android:endColor="@color/material_primary_700"
-        android:gradientRadius="400"
-        android:startColor="@color/material_primary_300"
-        android:type="radial" >
-    </gradient>
-</shape>

src/main/res/layout/layout_header.xml

@@ -1,15 +1,13 @@
 <?xml version="1.0" encoding="utf-8"?>
 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="wrap_content">
-    <android.support.v7.widget.AppCompatImageView
-        android:layout_width="match_parent"
-        android:layout_height="192dp"
+    <ImageView android:layout_width="match_parent"
+        android:layout_height="wrap_content"
         android:orientation="vertical"
         android:adjustViewBounds="true"
-        android:scaleType="fitXY"
-        app:srcCompat="@drawable/background_header" />
+        android:scaleType="fitCenter"
+        android:src="@drawable/background_header"/>
 
     <TextView xmlns:android="http://schemas.android.com/apk/res/android"
         android:id="@+id/drawer_title"