去掉启动界面logo显示，改成loading字符

welcome/src/main/res/layout/activity_welcome.xml

@@ -1,17 +1,17 @@
 <?xml version="1.0" encoding="utf-8"?>
-<layout xmlns:app="http://schemas.android.com/apk/res-auto">
+<layout>
     <android.support.constraint.ConstraintLayout
         xmlns:android="http://schemas.android.com/apk/res/android"
         android:id="@+id/activity_main_inference"
         android:layout_width="match_parent"
         android:layout_height="match_parent">
-        <ImageView
+        <TextView
             android:layout_width="match_parent"
             android:layout_height="match_parent"
-            android:src="@mipmap/welcome"
-            android:scaleType="centerInside" />
+            android:gravity="center"
+            android:text="Loading..."
+            android:textSize="32sp"
+            android:textColor="@color/black"/>
     </android.support.constraint.ConstraintLayout>
 
-    <!--未注册显示界面-->
-
 </layout>