MainFragment: Enable send file button.

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

@@ -62,8 +62,7 @@
                 android:text="@string/main_button_send_file"
                 app:layout_constraintLeft_toLeftOf="parent"
                 app:layout_constraintRight_toRightOf="parent"
-                app:layout_constraintTop_toBottomOf="@+id/button_hatchery"
-                android:enabled="false"/>
+                app:layout_constraintTop_toBottomOf="@+id/button_hatchery"/>
 
         <Button android:layout_width="wrap_content"
                 android:layout_height="wrap_content"